Displaying a united front, the two leaders in their 40s said in a statement they “support a strong, responsible, transparent multilateralism to face the global challenges.”
The pair were scheduled to hold formal talks and a private dinner on Wednesday, followed by a joint news conference early Thursday.
Those discussions are likely to focus on Trump's decision last week to impose punishing tariffs on imports of steel and aluminum from Washington's closest allies, including Canada, the European Union and Japan.
In retaliation, all of them have either hit back with their own tariffs on US goods or threatened to do so, as well as challenging the US trade measure at the World Trade Organization.
Both Trudeau and Macron had tried to persuade Trump not to impose the tariffs.
"There will be frank and sometimes difficult discussions around the G7 table, particularly with the US president on tariffs," Trudeau told reporters.
His private meeting with Macron, he said, "will be an opportunity to talk about the relations between Canada and France that are going very well, but also to highlight the challenges that we are going to have around the G7 table, and to make sure we are aligned."
Economic order 'under attack'
The EU and Canada were originally shielded from the aluminum and steel tariffs, but Trump ended that exemption last week.
Since then, Trudeau, Macron and other European leaders have toughened their tone, lamenting what they see as rising US protectionism.
"The world economic order is... under attack," Canada's Trade Minister Francois Philippe Champagne commented.
Trump economic advisor Larry Kudlow, however, framed the trade spat as a "family quarrel" which he said would be "worked out," while adding that his administration "will do what is necessary to protect the United States, its businesses and its workforce."
Macron -- who had formed an unlikely bond with Trump -- declined to characterize his last conversation with the US leader, but unnamed White House insiders told US media it was "terrible."
Still, the French leader pledged to have a "productive and frank discussion with President Trump at the G7," the Group of Seven industrialized democracies.
"It does not detract from the friendship we have for each other and the friendship between our two countries," he said.
Trudeau, who has been cordial with Trump, said in March he had received assurances that Canada would be spared as they worked toward a revamp of a 1994 continental trade pact with the United States.
But that all changed with the announcement of the US levies, and Trudeau retaliated with Can$16.6 billion (US$12.9 billion) in tariffs on US goods.
The two sides are also deadlocked on negotiations over the future of their North American Free Trade Agreement (NAFTA) with Mexico. Ottawa refuses to grant US demands for a clause that would end the trade deal after five years unless it is renewed by the parties.
Canada has also rejected "for now" a proposal floated by the White House for new separate US trade deals with Canada and Mexico.
The left-leaning Trudeau and Macron see each other as natural allies in a world increasingly shaped by right-wing nationalism. That bond should only grow deeper ahead of the G7 in Quebec.
According to a statement, they settled on the creation of an international working group to advance research and best practices in artificial intelligence, as well as a new defense alliance.
The French-Canadian Council for Defense Cooperation will meet by year's end and look at boosting cooperation between their respective armed forces, including conducting joint military operations and partnering on UN missions.
Focus on trade
The GSeven summit on Friday and Saturday in La Malbaie, a small town 140 kilometers (87 miles) from Quebec City, will bring together the leaders of Britain, Canada, France, Germany, Italy, Japan and the United States.
Trudeau hoped to put the focus on jobs, security concerns, cleaning up the world's oceans and empowering women. But officials concede the agenda is likely to be overtaken by trade disputes.
"I think it's fair to expect that any discussions on the global economy... in the current environment will quickly turn into a discussion about trade," a senior Canadian official said.
The other six members of the G7 are holding out hope they can find common ground with Trump, but are prepared to stand up to US protectionism.
"The challenge is to try to preserve a form of unity within the G7, but not hesitate to express firmly and strongly the interests of France and of Europe," Macron's office said.