The announcements come as Mr. Trump seeks to make headway on the deep US trade deficit, saying the country has been taken advantage of for too long, and he is fighting back.
While making no direct criticism of Mr Trump, she left no doubt that European Union nations will impose counter-measures on United States goods in response.
Navarro's interview followed another by National Economic Council Director Larry Kudlow, who called Trudeau's statement as "diplomatic betrayal".
"Kim must not see American weakness", Kudlow said.
After a pre-summit meeting of G-7 finance ministers, in which Washington was rebuked by the other six members on June 2, Treasury Secretary Steven Mnuchin said that despite sharp disagreements on trade, the other countries remain "our most important allies".
Yet, Mrs May insisted the United Kingdom "fully intends to honour the commitments" made at the G7, in spite of Mr Trump's withdrawal from the communique.
Canada's House of Commons on Monday unanimously condemned the personal attacks on Prime Minister Justin Trudeau by U.S. President Donald Trump and his surrogates as the famously polite nation simmered over the weekend broadsides by its U.S. ally.
Joining that view was Nicholas Burns, a former USA undersecretary of state under President George W. Bush, who called Canada "the best neighbor we could have".
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".
"What I saw Prime Minister Trudeau say was, I thought, fairly benign and certainly didn't warrant any attack".
In a tweet posted Saturday evening, Trump said his decision to rescind support for the statement was based on "false statements" made by Trudeau during a press conference he gave, as well as "the fact that Canada is charging massive Tariffs" on USA companies.
If these goods that originate in Canada and are eventually sold there without have been substantially worked upon in the United States are taken into account then Ottawa comes out the victor.
Mulroney has acted as an informal advisor on USA trade to Trudeau's Liberal government.
The President insists he has slapped the levies on to hit back at charges imposed by other countries and has accused his allies of trying to milk the Us's economy.
"We hope it doesn't come to that, but if the USA tariffs remain in effect, we will impose our tariffs on July 1", he said. "Our Tariffs are in response to his of 270% on dairy".
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 really kind of stabbed us in the back", Kudlow said.
The group of seven nations that make up the G7 are Canada, France, the United States, the UK, Germany, Japan and Italy.
The President ripped Trudeau on twitter over his "false statements" to the press; adding that he instructed his administration "not to endorse" a joint statement from the G7 countries following the contentious summit.
"There are more jobs now posted than there are people looking for work in the United States, and we've cut immigration pretty substantially", he said, noting that the country's birth rate is low.