Conservative Leader Stephen Harper says the Liberals are "living in in a dream world" if Justin Trudeau thinks his plan to cancel the procurement of F-35 fighter jets won’t hurt the Canadian aerospace industry, and NDP Leader Tom Mulcair agrees cancellation comes at a price.

Harper was reacting to the Liberal leader's announcement Sunday that he would scrap the F-35 purchase and instead put the savings toward the Royal Canadian Navy and shipyards in Halifax and Vancouver.

"The Liberal party is living in a dream world if they think we could pull out of the development project of the F-35 and not lose business," Harper told supporters in St. Jacobs, Ont., Monday morning. "I mean I don't know what planet they're living on."

He said the contract to build the F-35s, which would replace Canada’s aging CF-18s, "is critical to our aerospace industry."

But according to some experts, Harper may be "blowing smoke" with that claim.

"Justin Trudeau is right on this one," University of British Columbia political science professor Michael Byers told CTV News' Power Play on Monday.

"He knows full well that if a foreign company wins a contract in Canada for defence procurement, it is obligated to invest 100 per cent of the value of that contract in Canadian industry – these are called industrial regional benefits."

Harper also said on Monday that Trudeau's plan to invest in more shipbuilding to compensate for losses in aerospace makes no sense, as Canada is already doing lots of shipbuilding.

"All of our shipbuilders are up to their eyeballs in work because we have largest shipbuilding program in history," Harper said. "So he's not giving shipbuilding anything; he’s merely talking about cratering our aerospace industry, which is, as I say, bad policy."

When Trudeau was asked Monday whether he could promise that cancelling the F-35s would not result in extra costs, Trudeau reiterated his Sunday comments that there are other jets that can be purchased for less.

"There is no contract right now for the F-35s," he told supporters in Toronto, adding it no longer makes no sense – "if it ever did" – to have a stealth, first-strike capacity fighter.

"There are many other fighters at much lower price points that we can use that have been proven that we will be able to actually deliver in a timely way," he said.

Mulcair would be "a champion"

Mulcair told CTV Atlantic's Steve Murphy that both Trudeau and Harper have pre-judged the public tendering process underway.

"They both want to determine the outcome without a process," he said.

Mulcair added that "there have been problems" with the F-35s. "Let's not kid ourselves."

He questioned, for example, whether the jet would "work over the Arctic" or if it is "dangerous with only one engine."

Asked whether Trudeau was correct that the F-35 could be cancelled without a cost Canada's aerospace industry, Mulcair said "that's false," before again turning his attention to Harper.

"Do you know how many Conservative ministers attended the world’s biggest airshow at Bourget in Paris this year?" he said. "Not one, not even the industry minister."

"When Boeing wants to sell planes to China, President Obama goes to China to help Boeing," he added. "I want to be that champion for manufacturing in Canada."

The Conservatives' planned purchase of 65 F-35s was put on hold in December 2012 after the auditor general accused the government of fudging project costs and not doing sufficient research.

An independent audit by accounting firm KPMG found the purchase would have cost taxpayers an estimated $44 billion over its 42-year lifetime, including fuel, maintenance, and attrition costs. That was more than four times higher than the initial price tag of $9 billion.