OTTAWA -- Leaders from across Canada's political spectrum voiced their support Sunday for free trade and opposition to U.S. tariffs on steel and aluminum while denouncing the Trump administration's unprecedented attacks on Prime Minister Justin Trudeau.

Among them were some of Trudeau's fiercest critics, Conservative Leader Andrew Scheer and incoming Ontario premier Doug Ford, both of whom promised to stand with the government as it seeks to resolve what has become an all-out trade war with the U.S.

Former Canadian prime minister Stephen Harper, meanwhile, questioned Trump's "obsession with trade relations with Canada" during an appearance on U.S. television.

All of the comments came after Trump unleashed a Twitter tirade against Trudeau following the G7 on Saturday, in which the president called the prime minister "dishonest and weak."

Trump also threatened to go after Canada's auto industry, a mainstay of the Ontario economy, in the same way that he has already done with its steel and aluminum sectors.

The tirade was enhanced by extensive comments Sunday from two of the president's closest advisers who said the prime minister betrayed Trump in comments Trudeau made at the end of the G7 summit in the Charlevoix region of Quebec.

Trump's top economic adviser Larry Kudlow said Trudeau made Trump look weak ahead of his North Korea summit, while trade adviser Peter Navarro said there was a "special place in hell" for the prime minister.

"It's certainly not helpful to have that type of language when we're dealing with two governments, two countries that have had a long history of mutual support, mutual co-operation," Scheer told reporters during an event at an Ottawa gas station on Sunday.

"That's why we have been doing what we can to present that united front when we're talking about the benefits of NAFTA, when we're talking about the benefits of free trade for both Americans and Canadians."

That doesn't mean the Conservatives support everything the Liberals are doing, Scheer added before listing a number of "missed opportunities" to put pressure on the U.S. and make Canada more attractive to foreign investment.

Those include a failure to quickly ratify the 11-country free-trade deal known as the Trans-Pacific Partnership as well as the government's push for a national carbon tax and its refusal to cut taxes for businesses.

Nevertheless, he said, "every time in history when there are these types of discussions, all Canadians who believe in free trade, political parties who believe in the benefits of free trade as a philosophy, as an economic policy goal, have worked together.

"And that's what we are going to continue to do."

Ford, a populist campaigner who has praised U.S. President Donald Trump in the past, similarly said on Sunday that he stands "shoulder to shoulder" with Canada's Liberal prime minister because jobs in his province are at stake.

"My number 1 priority is to protect jobs in Ontario, especially protect the steel workers, aluminum workers. That's going to be a priority," Ford told reporters at Queen's Park.

"We're going to sit down with our federal counterparts. We're going to stand united. I know all provinces should be standing united with our federal counterparts and we'll deal with that."

Former prime minister Harper rounded out the conservative triumvirate during an appearance on the Fox news network in which he noted that the deep trade relationship between Canada and the U.S.

The U.S. has legitimate concerns about trade with China and even Mexico when it comes to automobiles, Harper added, "and I would be the first person telling our government to be a partner in those things because I think Canada shares those concerns."

However, he added, "I don't understand the obsession with trade relations with Canada."

Conservatives weren't the only ones offering support as Green Party Leader Elizabeth May tweeted that the prime minister was handling Trump's "outbursts" and "bullying" as well as anyone, and "all Canadian leaders need to support Trudeau."

And NDP MP Charlie Angus tweeted that Trump's behaviour was "appalling," adding: "This is a small-minded man not fit for public office. Canada will not be pushed around by his circus-thug bluster."

Not everyone was impressed, however, as Conservative Sen. Leo Housakos accused the prime minister of using an "incompetent approach" to dealing with the U.S., in part by refusing to pursue one-on-one trade talks with Washington.

"Stop poking U.S., stop jumping in front of bullets meant for Mexico, start bilateral (NAFTA negotiations) and stop dialogue with Iran," Housakos said on Twitter.

"Focus on (a) deal that's critical to our economy."

Former Canadian ambassador to the U.S. Derek Burney was among those urging Canada and others to stay calm, adding that he hopes Trump's latest antics will spark more "sober sentiments" in Congress and with others in the U.S.

Several members of Congress and former U.S. officials were quick to express their disapproval with the administration's attacks on Trudeau and Canada, including Republican Sen. John McCain and Democratic Sen. Chris Murphy.

Murphy retweeted a comment by European Council President Donald Tusk who appeared to mock Navarro by stating: "There is a special place in heaven for (Trudeau). Canada, thank you for the perfect organization of (the) G7."