"If they retaliate, they're making a mistake", Trump declared.
Speaking at a post-summit press conference, Trudeau acknowledged that there were major differences with Trump.
"What we did this weekend was come together, roll up our sleeves and figure out a consensus language that we could all agree to", Trudeau said in the town of La Malbaie where leaders have been meeting since Friday morning.
And he was also asked for his thoughts on what Trump's move could mean for the future of the G7.
"We're the piggy bank that everybody is robbing".
"The level of relationship is a 10", Trump said.
Trump, who argues his tariffs are meant to protect USA industry and workers from unfair global competition, told reporters he had suggested to the other G7 leaders that all trade barriers, including tariffs and subsidies, be eliminated.
Trump set the tone before leaving Washington on Friday.
That communiqué contains commitments on exchanging approaches for fair tax systems and fighting tax evasion, fighting protectionism, reducing trade barriers, establishing strong health systems, promoting growth in developing economies, and ending sexual and gender-based violence, among other issues.
The US has slapped a 25% tariff on imports of steel and 10% on aluminium from countries including the United Kingdom and the rest of the European Union.
Trump's anger seems to stem from a press conference Trudeau held where he said he would with "absolute certainty" impose retaliatory tariffs on the United States. "We'll see how it all works out", he said, referring specifically to Canada.
He said unleashing retaliatory measures "is not something I relish doing" but that he wouldn't hesitate to do so because "I will always protect Canadian workers and Canadian interests".
French President Emmanuel Macron responded in a "courteous but very firm tone" to present the European side of the story, and Japanese Prime Minister Shinzo Abe chimed in as well, the official said. Trump fired back, saying the USA had been duped for for years by barriers and that any country that imposed its own measures would regret it.
But in a tweet after flying out of Canada, the United States president showed he was in no mood to back down in any trade dispute.
"We are focused on everything we accomplished here at the #G7 summit", spokesman Cameron Ahmad said.
Fox Business contributors James Freeman and Kristina Partsinevelos discuss President Trump's upcoming meeting with North Korean Leader Kim Jong Un and the president's recently imposed tariffs. France will host next year and the United States in 2020.
"He won't have that opportunity again", Trump said.
Merkel said European Union countries at the summit agreed that the conditions to readmit Russian Federation had not been met and even Moscow seemed to reject the suggestion.
But unanimous agreement by all G7 leaders on two big environmental issues at the 2018 summit eluded Trudeau, hosting the club of advanced industrialized nations for the first time amid tensions stirred by Trump.