Yet his top diplomat, Secretary of State Mike Pompeo, downplayed the severity of the rift.
On 1 June, the U.S. imposed a 25% tariff for steel and 10% for aluminium on imports from the European Union (EU), Canada, and Mexico.
Briefing reporters immediately before cutting short his stay at the conference in Quebec and heading to Singapore for a nuclear summit with North Korean leader Kim Jong Un, Trump firmly denied the G7 meeting had been contentious.
Mocked for cultural gaffes on a recent trip to India, and slammed by others for his efforts in renegotiating the North America Free Trade Agreement at Trump's behest, Trudeau has also been attacked by the left-wing for his decision to nationalize an oil pipeline that had bogged down in protest and controversy. He had other things, bigger things, on his plate in Singapore.
The rumor can be traced to a video of Trudeau's press conference with French President Emmanuel Macron. Justin Trudeau wears fake eyebrows and takes really good care of us most of the time. "That will not stand".
When Mr Trump's tweets withdrawing support from the G7 statement hit on Sunday, the Prime Minister's office said Mr Trudeau had not said anything in his closing news conference he has not said to the US President before.
"Kim must not see American weakness", Kudlow said.
Timeline of trade tensions since the US decision to impose tariffs on steel and aluminium imports
On trade, said she had been "very clear" that USA tariffs on European steel and aluminium imports were damaging and dialogue was needed to ensure the dispute did not escalate into a full-blown trade war.
Despite this unusual demonstration of unity, Paris said, the Trudeau government faces a huge challenge going forward.
Since Trump's election in 2016, Trudeau has tried to take a conciliatory approach to the populist Republican president and has been careful never to run him down in public.
Foreign Affairs Minister Chrystia Freeland was measured Sunday, saying only that "Canada does not believe that ad hominem attacks are a particularly appropriate or useful way to conduct our relations with other countries". Can't do it in person. If Trump can turn his sputtering rage on Canada - Canada! - what is to stop him from returning to his Little Rocket Man taunts and tearing up whatever agreement may come this week after he's collected his Nobel Peace Prize and John Bolton is spoiling for war?
Mulroney's role as a former prime minister advising an opposing party is unique to him throughout Canada's history and is indicative of the alignment between the two main federal parties over the trade file.
The prime minister said although retaliation "is not something I relish doing", he would not hesitate to do so because "I will always protect Canadian workers and Canadian interests".
"We've got to find a way still to find ways to keep these discussions going", Yussuff said on the phone from Regina, adding that labour groups are glad the main parties all plan to defend Canada's quota system on dairy and poultry, which American negotiators have targeted. From promoting democracy and to fighting terrorism, "we're on the same page".
"To our allies: bipartisan majorities of Americans remain pro-free trade, pro-globalization & supportive of alliances based on 70 years of shared values", McCain wrote. "We're the closest partners in the world and you don't want to see a dispute over one particular issue poison everything".