Trump swiftly responded to Trudeau by upending the communiqué in a series of tweets Saturday evening.
He injected additional controversy by suggesting that the G7 offer a seat at the table to Russian Federation, which was ousted from the group after it annexed Crimea.
Reacting to Mr Trump's tweets, Mr Trudeau's office said: "We are focused on everything we accomplished here at the summit".
Trump's recent moves, building on 18 months of nationalist policy-making, leave him out of step with the globally-minded organization and have prompted speculation that the group could fracture into something more like the "G6 plus one".
Earlier in the day, Trump had said there should be "tariff free" trade between the G-7 nations, though he did not elaborate on how or whether the United States would reduce barriers.
Trump and Trudeau have been ramping up insults ― with Trump characteristically going further than Trudeau ― as the two countries bicker over tariffs.
Still, the fundamental differences remained clear.
Earlier this year, Mr Trump had criticised India over import duty on the iconic Harley-Davidson motorcycles and had threatened to increase the import tariff on "thousands and thousands" of Indian motorcycles to the US. "I don't understand the obsession with trade relations with Canada", he said, given that Canada is the biggest single buyer of American goods and services in the world.
Mr Trump has also attacked Mr Trudeau personally, suggesting the Canadian prime minister is "very dishonest and weak" and "acts hurt when called out". A Canadian official said the leaders discussed accelerating the pace of the talks. Her interview came about a day after Trump refused to endorse the G7 summit's communique that called for reducing tariff barriers. But lo, by the time I landed in Hong Kong to change flights I read that there was a joint communique. The European Union also attends. He said Canada has to stand up for itself.More news: Forza Horizon 4 Revealed with Brand New Trailer
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Merkel said she was disappointed that Italy's new prime minister, Giuseppe Conte, endorsed Trump's call on Russian Federation before consulting with other European powers.
Before arriving at the Quebec summit, Trump injected fresh drama by asking why Russian Federation wasn't included in the group.
Yet the US President and his aides have lashed the leader of America's neighbour, longtime ally, Five Eyes member and G7 Summit host with language usually reserved for rogue nations just before the bombs begin to fall.
Russian Federation has been shut out since its 2014 annexation of the Crimean peninsula from Ukraine, and has since earned Western condemnation for its military intervention in Syria in support of dictator Bashar al-Assad.
Germany's Angela Merkel later described Mr Trump's decision to reject the joint communique initially agreed between the G7 leaders as "sobering" and "depressing".
The comments drew a mixed response.
Canada's foreign minister, Chrystia Freeland, said her country "does not conduct its diplomacy through ad hominem attacks".
"We asked him about that", she told Anne Will, adding that his answers "did not sound convincing" to her.
"There is a special place in hell for any for leader that engages in bad faith diplomacy with President Donald J. Trump and then tries to stab him in the back on the way out the door and that's what bad-faith Justin Trudeau did with that stunt press conference, that's what weak, dishonest Justin Trudeau did", Navarro said on "Fox News Sunday".