Kudlow accused Canada Sunday of making polarizing comments about the United States' trade policy, and said that Trump had to pull out of the joint scommunique because the Canadian prime minister has "stabbed us in the back".
The attack on a longtime ally and its leader drew sharp criticism.
And in Ottawa on Monday, International Trade Minister Francois-Philippe Champagne urged lawmakers to speed ratification of the Trans-Pacific Partnership that might offset losses in United States trade by binding Canada closer to Asia, Australia and Latin America.
Trump had earlier called Trudeau's statement as "dishonest and weak".
Trump went on to say that the U.S. gets "unfairly clobbered" on trade despite "protecting Europe at great financial loss". He had other things, bigger things on his plate in Singapore, he said.
"Germany pays 1% (slowly) of GDP towards North Atlantic Treaty Organisation, while we pay 4% of a MUCH larger GDP".
But Trudeau's absence was also likely part of a deliberate strategy to not add fuel to the Trump fire.
Trump said he chose to back out of the G7 communique after watching Trudeau's closing summit news conference, at which he warned that Canada would not be pushed around on tariffs - a point the Canadian prime minister had made several times before.
Trudeau, on the June 3 episode of NBC's "Meet the Press", uses stronger words to characterize Trump's tariffs - "The idea that Canadian steel that's in military vehicles in the United States, that makes your fighter jets is somehow now a threat ... the idea that we are somehow a national security threat to the United States is quite frankly insulting and unacceptable".
For his comments, Trump fired back on Twitter, stating, "Please tell Prime Minister Trudeau and President Macron that they are charging the USA massive tariffs and create non-monetary barriers".
Navarro, the Trump trade adviser, said his harsh assessment of what "bad faith" Trudeau did with "that stunt press conference" on Saturday "comes right from Air Force One".
Mrs May later said in her statement: "The UK fully intends to honour the commitments we have made". Can't do it in person.
Trudeau said he had reiterated to Trump, who left the G-7 meeting before it ended, that tariffs would harm industries and workers on both sides of the U.S.
British Prime Minister Theresa May "is fully supportive" of Trudeau and his leadership, a senior United Kingdom government source said, while European Council President Donald Tusk tweeted: "There is a special place in heaven for @JustinTrudeau". From promoting democracy and to fighting terrorism, "we're on the same page. We're the closest partners in the world and you don't want to see a dispute over one particular issue poison everything".
Lucey reported from Singapore and Gillies from Quebec City. It came in sharp contrast to a roar of disapproval among Canadian politicians, who banded together across party lines to denounce Trump's attack and praise the bilateral and trading relationship between the two neighbors.