The Canadian government is preparing billions of dollars in retaliatory measures on U.S. exports to Canada if President-elect Donald J. Trump makes good on a threat to impose tariffs on Canadian goods, setting up a potential showdown between two countries that are each other’s largest trading partners.

Canada is assembling a list of measures, including tariffs on U.S. exports to Canada and levies or other restrictions on key Canadian exports to the United States, if Mr. Trump imposes a sweeping 25 percent tariff on Canadian goods.

But the government made clear that it will wait to see what Mr. Trump might do before responding.

“Everything is on the table,” Prime Minister Justin Trudeau said during a news conference in Ottawa, flanked by senior members of his government and the leaders of most of Canada’s provinces and territories. Mr. Trudeau spent most of Wednesday discussing with provincial leaders how to best prepare for potential U.S. tariffs.

For now, Canada’s government is working under the assumption that Mr. Trump is serious about tariffs, which he has linked to the flow of undocumented migrants and drugs across the U.S.-Canada border.

Canada has already announced a series of steps meant to beef up the border, including more personnel and technology. The government on Wednesday said it was also deploying Blackhawk helicopters and more drones to bolster the surveillance of the shared border.

But in more recent weeks Mr. Trump has made statements suggesting that his motivation for possible tariffs on Canadian goods may not be solely about border security. The president-elect has repeatedly spoken about Canada becoming another U.S. state, even threatening economic force to annex the country.

Mr. Trump has argued that Canada has a trade surplus with the United States, while the United States provides important defense guarantees to Canada, to make a case that the relationship favors Canada and that the imbalance needs to be addressed.

Mr. Trump’s comments have been met with incredulity and outrage among Canadian political leaders.

Any tariffs would violate a trade agreement among the United States, Mexico and Canada, originally known as NAFTA (North American Free Trade Agreement), which was renegotiated during Mr. Trump’s first presidency. It is scheduled to be renewed next year, but the introduction of tariffs by any country would violate the agreement, potentially rendering it moot.

Mr. Trudeau, on Wednesday, said that Canada was prepared meet any aggressive economic moves by the incoming Trump administration with equal aggression.

“I support the principle of a dollar-for-dollar response,” Mr. Trudeau said. Officials said that this could lead Canada to impose tariffs on hundreds of billions of dollars’ worth of goods exported to the United States.

Canada could impose tariffs on key U.S. imports such as orange juice, officials have said, although Mr. Trudeau on Wednesday acknowledged that tariffs imposed by either government would ultimately hurt both countries and their consumers.

The debate over how to handle the potentially crippling tariffs have strained the relationship between Canada’s federal government in Ottawa, the capital, and its powerful provincial leaders.

While most premiers have united behind Mr. Trudeau and tried to project a “Team Canada” approach, some have struck a contrarian note.

Danielle Smith, the leader of the province of Alberta, which is a key source of oil for the United States, has repeatedly said she would not agree to having her province’s key resource be disrupted, even if targeting oil exports to the United States strengthens Canada’s negotiating hand.

Ms. Smith, who went to Mar-a-Lago to meet Mr. Trump on her own this week, attended Wednesday’s meeting remotely and did not sign a joint statement issued by provincial leaders and Mr. Trudeau. Instead she issued her own statement.

“Federal government officials continue to publicly and privately float the idea of cutting off energy supply to the U.S. and imposing export tariffs on Alberta energy and other products to the United States,” Ms. Smith said in a post on X. “Until these threats cease, Alberta will not be able to fully support the federal government’s plan in dealing with the threatened tariffs.”

Mr. Trudeau, members of his government and premiers from other provinces have made clear that tariffs on oil exports need to remain on the negotiating table as a possible lever to pressure the Trump administration.

About 80 percent of Canada’s oil is exported to the United States, which relies on Canada for more than half of its oil.

If Canada moves to retaliate with its own tariffs, “it has to be fair across the country,” Mr. Trudeau said.

Mr. Trudeau this month announced plans to resign by early March, when his party, the Liberals, selects a new leader who will also become prime minister. The country is expected to head to federal elections soon after, sometime in the spring, putting an essentially lame-duck leader in charge during the first phase of the new Trump administration.

After 15 months of bombardment and suffering, the prospect of a cease-fire and a hostage release deal in Gaza provides Palestinians and Israelis with a glimmer of jubilation, but it’s a view tinged with uncertainty.

For Palestinians, the agreement, if it is finalized, is likely to offer at least several weeks of respite from a devastating Israeli military campaign that has killed more than 45,000 people in Gaza, both civilians and combatants.

For Israelis, it could allow for the release of at least one-third of the remaining hostages held by Hamas and its allies. The captives were taken when Hamas raided Israel on Oct. 7, 2023, the first of 466 days of war.

But the ambiguity of the deal, drafts of which were reviewed by The New York Times, also means lingering unease and the possibility of renewed conflict within weeks. To persuade both sides to sign on, mediators forged an arrangement that is worded so loosely that some of its components remain unresolved, meaning that it could easily collapse.

In the first six weeks of the deal, Hamas is expected to release 33 hostages in exchange for several hundred Palestinian prisoners held by Israel. Israel is also meant to gradually withdraw its troops eastward, allowing for hundreds of thousands of displaced Palestinians to return home.

For the deal to last longer than six weeks, Israel and Hamas still need to resolve certain issues, including the terms by which Hamas will release the approximately 65 other hostages, some of whom are believed to be dead, in its custody. To prolong the truce, both sides would also need to agree to end the war entirely, while Israel would need to withdraw from strategic areas of Gaza — moves that are opposed by key members of Israel’s ruling coalition.

Should those talks break down, the war could continue after a 42-day truce, if not earlier.

That means the coming weeks will remain fraught for the families of the Israeli hostages who will likely not be released in the deal’s first phase. Gazans will live with the possibility that Israel’s strikes could continue.

This precarity also presents potential peril for both Hamas and Benjamin Netanyahu, Israel’s prime minister.

If war resumes, a severely weakened Hamas might finally lose its grip on Gaza. But if the deal becomes permanent, Hamas would have a greater chance of retaining power in the territory — a symbolic victory for a group that at one point seemed close to ceding its 17-year rule.

An outcome that leaves Hamas in control could prove damaging to Mr. Netanyahu, whose far-right coalition partners have threatened to leave his coalition if Hamas survives, a departure that would destabilize and potentially collapse his government.

For months, Mr. Netanyahu has avoided an arrangement that would risk such a threat to his power. The ambiguity of the deal is partly the result of his need to present it as only a temporary arrangement.

The coming weeks could help clarify whether the prime minister feels politically strong enough to face down his coalition partners. Even if he does, other shoals await: The end of the war will likely lead to a national inquiry about Israel’s security failures on Oct. 7, 2023, possibly uncovering revelations that could damage Mr. Netanyahu as well as his security chiefs.

Despite these uncertainties, analysts say, the deal still stands a reasonable chance of becoming permanent. The loose language of the agreement would allow the cease-fire to drag on as long as the two sides remain locked in negotiations, even if those negotiations take longer than six weeks to reach further agreement.

And both sides have reasons to keep extending the negotiations, however fruitless the talks.

Hamas, isolated and weakened, wants to remain dominant in Gaza, and a cease-fire allows it time to recuperate.

Mr. Netanyahu has long hoped to forge landmark diplomatic ties with Saudi Arabia. Negotiations for such a deal, which were derailed by the outbreak of war in 2023, would likely only resume if the truce holds.

A Saudi-Israel deal “can’t happen with an ongoing war in Gaza, with large numbers of Palestinian casualties, Hamas holding Israeli hostages and a worsening humanitarian catastrophe,” said Aaron David Miller, a fellow at the Carnegie Endowment for International Peace, a Washington-based research group.

Similarly, a large protest movement in Israel is pushing Mr. Netanyahu to extend the deal in order to release every hostage; such public pressure could ultimately drown out any backlash he faces for ending the war. The euphoria and celebration that is expected to accompany each hostage release may also accelerate momentum and public support in Israel for a permanent arrangement that leads to freedom for every captive.

The role of the Trump administration will also be crucial. Mr. Trump’s Middle East envoy, Steve Witkoff, played a key role in recent days in pushing Israel toward a deal, officials say, and the administration’s continued interest may decide how long the deal lasts.

“Trump is going to be the critical variable when it comes to the Israeli side,” said Michael Koplow, an analyst at Israel Policy Forum, a New York-based research group.

“If Trump is happy with having orchestrated the first phase and then moves on to other issues, it will be harder to keep the cease-fire in place,” Mr. Koplow said.

If Mr. Trump retains his focus, “it will be tougher for Netanyahu not to find ways to extend the cease-fire deal and figure out other ways to appease his disgruntled coalition members,” Mr. Koplow added.

Johnatan Reiss contributed reporting from Tel Aviv.

When President-elect Donald J. Trump’s Middle East envoy, Steve Witkoff, met with Prime Minister Benjamin Netanyahu of Israel on Saturday to pressure him on a cease-fire deal in Gaza, there was someone on the speakerphone: Brett H. McGurk, President Biden’s longtime Mideast negotiator.

It was a vivid example of cooperation between two men representing bitter political rivals whose relationship has been best described as poisonous. Rarely if ever have teams of current and new presidents of different parties worked together at such a high-stakes moment, with the fate of American lives and the future of a devastating war hanging in the balance.

“Brett is in the lead,” Mr. Witkoff said last week at Mar-a-Lago, Mr. Trump’s club in Florida, describing the working relationship. That description was accurate by all accounts, even if it did not match what Mr. Trump had said moments before in one of several statements describing his negotiators as critical players.

In fact, Mr. Trump’s threat that “all hell” would break loose if no deal was reached before his inauguration on Monday might have helped motivate Hamas’s leadership to make final decisions. But people familiar with the negotiations said the announcement on Wednesday of a deal to temporarily end hostilities in Gaza was the result of months of work by Mr. McGurk in the Middle East, capped off by several weeks of carefully coordinated efforts by Mr. Witkoff.

Mr. Witkoff, a blunt real estate investor from the Bronx, has largely planted himself in Qatar for the negotiations, knowing that whatever Mr. McGurk negotiated, he would have to execute. In fact, the 33 hostages who will be released under the cease-fire deal may not see freedom until Inauguration Day or after. The cease-fire would expire six weeks later, unless Phase 2 of the agreement kicks in.

By design, the goal was to send a single, unified message that the fighting must end and the hostages held by Hamas must be released. One person familiar with the negotiations, who spoke on the condition of anonymity to describe the discussions, said Mr. McGurk was more involved in hammering out details of the agreement, while Mr. Witkoff’s role was to make clear that Mr. Trump wanted a deal by the time he is inaugurated.

The president-elect has also been setting some early parameters in his dealings with Mr. Netanyahu — who, for all his support of Mr. Trump in the election, was perceived by the Trump camp as dragging his feet on a deal. Mr. Witkoff flew to to Israel from Doha on Saturday — despite the Sabbath — to underscore the message that Mr. Netanyahu had to get on board.

Mr. Witkoff’s work, including the meeting with Mr. Netanyahu, helped Mr. McGurk and the Biden administration to put pressure on both sides during the negotiation, according to the person familiar with the talks.

It was not at all clear that such an arrangement would work in the days immediately after Mr. Trump won a second term.

He and Mr. Biden have barely talked in recent weeks, their already acrimonious relationship weighed down by the Trump team’s determination to clean out the White House career staff and the Biden team issuing last-minute orders to box in the new administration.

The exception has been the Gaza negotiations, according to people on both sides.

One called it a “very close partnership” between Mr. McGurk and Mr. Witkoff and said the result had been an “incredibly effective” process by which the Biden administration finalized a deal that the Trump administration would have to oversee.

That cooperation began soon after Mr. Trump won the election and named Mr. Witkoff to be his envoy to the region. Biden administration officials have said they believe the momentum for a deal began before that, when Mr. Biden helped broker a separate agreement to end fighting between Israel and Hezbollah in Lebanon. That isolated Hamas and helped persuade the group that a cease-fire was in its interests, according to Biden administration officials.