When President Trump last attended a Group of 7 meeting in Canada, he was in many ways the odd man out.

At that meeting, in 2018, Mr. Trump called for the alliance of Western countries to embrace Russia, antagonized allies and ultimately stormed out of the summit over a trade battle he began by imposing metals tariffs on Canada.

As he returns on Sunday for the Group of 7 meeting in Alberta, those fissures have only deepened. Since retaking office, the president has sought to shrink America’s military role abroad and made threats to annex the summit’s host after embarking on a much more expansive trade war.

Mr. Trump is now facing a self-imposed deadline of early July to reach trade deals. His trade adviser even promised in April that the tariffs would lead to “90 deals in 90 days.” Despite reaching framework agreements with Britain and China, the administration has shown scant progress on deals with other major trading partners.

The future of the president’s favored negotiating tool is uncertain as a legal battle over his tariffs plays out in the courts. But a failure to reach accords could lead the Trump administration to once again ratchet up tariffs and send markets roiling.

“I think we’ll have a few new trade deals,” Mr. Trump told reporters at the White House on Sunday as he left for the summit.

The gathering also comes amid fears of a broader, regional war in the Middle East after Israel launched a surprise attack on Iran’s leadership and nuclear facilities last week, prompting both nations to trade strikes.

“Sometimes they have to fight it out, but we’re going to see what happens,” Mr. Trump said when asked what he was doing to de-escalate the conflict between Israel and Iran. “I think there’s a good chance there will be a deal.”

Mr. Trump’s aides say he will discuss a range of topics, including fairness in global trade, critical minerals, illegal migration, drug smuggling and international security. World leaders will also be focused on surging oil prices and Russia’s war against Ukraine.

Leaders of the Group of 7 nations — Britain, Canada, France, Germany, Italy, Japan and the United States — will convene in Kananaskis, a remote town west of Calgary. The summit this week, the 50th such meeting, is usually a forum for the U.S. president to leverage allies and partners to further its agenda and assert its leadership on global issues of consequence.

But world leaders appear to be bracing for Mr. Trump’s shift away from global partnerships. Canadian officials have said that they were scrapping hopes of issuing a joint communiqué, the traditional statement leaders put out at the end of such meetings. Mr. Trump refused to endorse the joint statement moments after it was released at the end of the 2018 summit.

“One thing that the G7 represents just beyond the world’s largest economies is a community of shared values — shared values that Trump doesn’t necessarily share or subscribe to,” said Rachel Rizzo, a nonresident senior fellow at the Atlantic Council’s Europe Center.

Beyond trade, the war in Ukraine is likely to be a point of contention at the summit. While Mr. Trump has signaled reluctance to stay engaged in the war and derided multilateral organizations like NATO, European allies have rallied around Ukraine.

President Volodymyr Zelensky of Ukraine is expected to be in attendance.

François-Philippe Champagne, Canada’s finance minister, said the presence of Ukraine was meant to “send a strong message to the world,” that the Group of 7 was recommitting to support Kyiv and hold Moscow accountable.

At the 2018 summit in Canada, one of the biggest disputes between Mr. Trump and allies was when he demanded Russia’s readmission to the Group of 7 nations. The country was ousted from the diplomatic forum after Mr. Putin violated international norms by seizing parts of Ukraine in 2014.

Since returning to office, Mr. Trump has boasted about his close relationship with Mr. Putin, and has repeatedly taken his side in the war — even falsely accusing Ukraine of starting it. Thus far, his embrace of Mr. Putin has not helped broker peace in the war.

“Given Trump’s ongoing conversations with Russian President Vladimir Putin, the prospect of any meaningful new G7 action to promote a durable resolution of the three-year-old conflict is highly uncertain,” Matthew P. Goodman, the director of the Greenberg Center for Geoeconomic Studies at the Council on Foreign Relations, wrote last week.

He said Mr. Trump’s attendance at the summit and his decision to impose tariffs on the other members had “cast a deep shadow over the gathering in Canada.”

Mr. Trump’s increased hostility toward U.S. allies is perhaps most exemplified by the relationship with the host country.

The relationship between the neighbors and top trading partners has been at a historical low since Mr. Trump’s re-election because of his decision to impose tariffs on Canadian goods and his continuing to threaten its sovereignty by asserting that Canada should be a part of the United States.

Prime Minister Mark Carney of Canada has sought a cordial relationship with Mr. Trump, but during a meeting in the Oval Office last month delivered a stern response to Mr. Trump’s suggestions: Canada “won’t be for sale, ever.”

“Never say never,” Mr. Trump replied.

Kori Schake, a former defense official in the George W. Bush administration who directs foreign and defense policy studies at the American Enterprise Institute, said that Mr. Trump’s treatment of Canada was “emblematic of the bullying Trump considers appropriate.”

“If this is the behavior toward a country with which we share a 5,500-mile border and a common air defense, it’s sure to be similarly antagonistic to other allies,” Dr. Schake said.

A May poll showed that Canadian sentiment toward the United States was at a historical low. Nine out of 10 Canadians rejected Mr. Trump’s idea of making their country the “51st state.” And recent travel data showed that Canadians were canceling or changing plans to visit the United States.

Canadians have been so galvanized against Mr. Trump that the rift appeared to have swung national elections. After Canada seemed poised to elect a conservative as prime minister in its April elections, the pendulum swung in favor of Mr. Carney, a liberal, by 30 percentage points, because the conservative candidate was seen as too close to Mr. Trump.

Still, while protests are expected during the summit, Alberta is a conservative stronghold within Canada, so Mr. Trump will find some friendly welcome there. Sometimes referred to as “Canada’s Texas” on account of its oil riches and conservative politics, Alberta is in the middle of a push to hold a secession referendum.

Mr. Carney, who this year holds the Group of 7 presidency, has invited the leaders of several nonmember countries: India, Brazil, South Africa, Mexico, Ukraine, Australia and South Korea, and the head of NATO.

In his second term, Mr. Trump has had explosive clashes in the Oval Office with Mr. Zelensky and Cyril Ramaphosa, the president of South Africa.

Michael Froman, the president of the Council on Foreign Relations, said that while the United States had historically played a role as a consensus builder at Group of 7 summits, it had often come to the table with a different perspective than its allies.

Mr. Froman argued that Mr. Trump was engaging the world, just under different terms than his predecessors.

“On some of these issues, we are currently alone,” Mr. Froman said.

“But I think one of the goals will be to bring other countries in our direction,” he added, “whether that’s through careful diplomacy” or “the threat of tariffs and sanctions.”

Matina Stevis-Gridneff contributed reporting.