Trump created a distraction when he walked in late for Saturday's breakfast meeting during the Group of Seven summit of leading industrialized nations being held in Quebec.
Trump, who is on his way to Singapore for a summit with North Korea's leader, also reiterated warnings that his administration was mulling tariffs "on automobiles flooding the USA market" in a move that would be primarily aimed at another G7 member, Germany.
Trump - who left the G-7 summit and headed to Singapore for his planned summit with North Korean leader Kim Jong Un - lashed out at Trudeau after revoking US endorsement of the communique, dubbing the Canadian prime minister "meek and mild". John McCain (R-Ariz.) criticized President Donald Trump's foreign policy with a message of allegiance to the United States' allies on behalf of Americans.
Trump had told Trudeau any retaliation would be a mistake and the prime minister agreed that it was "not something we want to do".
"I think it would be an asset to have Russian Federation back in, I think it would be good for the world, I think it would be good for Russian Federation, I think it would be good for the United States, I think it would be good for all the countries of the current G7", he said.
"Canadians, we're polite, we're reasonable, but we also will not be pushed around", Trudeau said.
Mr Trudeau's office, reeling from the abrupt Trump reversal hours after the two men had joked and smiled their way through a fractious G7 meeting, said only that Mr Trudeau had said nothing in his news conference that he hadn't said before.
But in meetings with Canadian Prime Minister Justin Trudeau and French President Emmanuel Macron, Trump stressed his friendships with the allies while continuing to insist he wanted to see changes on trade. Canadians, he said, "will not be pushed around".
Trump did not indicate that he had received any concessions in his negotiations on trade at the summit. "Or we'll stop trading with them". "So I'm very happy", Trump said, as the room erupted in laughter. Representatives from other G-7 countries said they felt as though they had made progress in conveying their positions to Trump, something many of them felt pressured to do by voters at home.
"And we charge nothing", Trump said.
Canada has managed supplies of dairy, eggs and poultry since the 1970s, restricting how much farmers can produce and limiting imports through onerous tariffs.
Mr Trump recently slapped tariffs on Canada, Mexico and the European Union, angering his counterparts before he arrived at the summit.
The president also offered reassurance that Canada and the USA have made progress in their trade dispute over his administration's punishing steel and aluminum tariffs on all the other G7 members. Trump said he thinks the group will produce a joint statement.
He said Saturday that he's also considering scrapping the North American Free Trade Agreement in favor of bilateral trade deals with Canada and Mexico individually.
"No tariffs, no barriers, that's the way it should be, and no subsidies", he said, warning that other countries could lose access to the United States if they don't reduce trade barriers. Europe's answer must be to stick even closer together, defend its interests and strengthen alliances with countries such as Japan and Canada, he said.