Yet after leaving the summit, Mr Trump tweeted that he would instruct USA officials not to endorse the G7 statement, after objecting to comments from summit host Mr Trudeau.
He pledged to impose retaliatory tariffs against the US, adding Canada "will not be pushed around".
"I have made it very clear to the President that it is not something we relish doing, but it something that we absolutely will do", Mr. Trudeau said.
Trudeau told the president that Canadians did not take it lightly that the USA has moved forward with significant tariffs on their steel and aluminum industry.
That decision was "kind of insulting" to Canadian veterans who had stood by their United States allies in conflicts dating back to the first world war, Trudeau said.
Kudlow lashed out at Trudeau first during an appearance on CNN's "State of the Union".
Trump's announcement on Twitter, after he left the G7 summit in Canada early, that he was backing out of the joint communique torpedoed what appeared to be a fragile consensus on a trade dispute between Washington and its top allies.
In a flurry of tweets from Air Force One, Trump - on his way toa meeting in Singapore with North Korean leader Kim Jong Un - also announced that he was withdrawing his support from the declaration.
Larry Kudlow said Mr. Trump negotiated in good faith with fellow global powers in Quebec. And then Trudeau starts blasting him in a domestic news conference? The European leaders sought to show unity against Trump and prod him into concessions on the tariffs, or at least an agreement to talk more about them.
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Following the G7 leaders summit, Prime Minister Justin Trudeau held a press conference criticizing USA tariffs and said that Canada "will not be pushed around".
"POTUS is not going to let a Canadian prime minister push him around", he said.
Mr Trudeau had told reporters that Mr Trump's decision to invoke national security to justify United States tariffs on steel and aluminum imports was "kind of insulting" to Canadian veterans who had stood by their USA allies in conflicts dating back to World War I.
Trump called Trudeau "dishonest & weak" after Trudeau said at a news conference that Canada would retaliate for new USA tariffs.
"As Canadians, we are polite, we're reasonable, but also we will not be pushed around,"Trudeau said".
Trudeau didn't respond to questions about Trump when the prime minister arrived at a Quebec City hotel on Sunday for meetings with other world leaders.
Navarro, Trump's top trade adviser, in an appearance on Fox News, declared Trudeau's comments "one of the worst political miscalculations of a Canadian leader in modern Canadian history".
Trump negotiated in good faith on the communique agreed by the other members of the G7, only to have Trudeau criticize USA policy after he left, Kudlow said.
Russian Federation was kicked out of the group in response to its 2014 annexation of Crimea. 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.
"For us, it was important that we have a commitment for a rule-based trade order, that we continue to fight against protectionism and that we want to reform the WTO", Ms Merkel told reporters.