TORONTO -- NDP Leader Tom Mulcair opened the post-Labour Day phase of the election campaign Tuesday night by injecting a little more Justin Trudeau into his stump speech.

Mulcair highlighted what he called the Liberal leader's "inexperience" at a rally in downtown Toronto, the heart of a crucial battleground for all major parties ahead of the Oct. 19 election.

He was clearly trying to differentiate himself from his rival on the centre-left as polls point to a tight, three-way race that also includes Conservative Leader Stephen Harper.

Mulcair criticized Trudeau for voting for a $15-an-hour federal minimum wage and then campaigning against it.

He also targeted Trudeau for announcing a Liberal government would run several years of deficits, and for voting in favour of the Harper government's anti-terrorism legislation -- Bill C-51 -- after initially opposing it. Trudeau has pledged to amend Bill C-51, if elected.

"Is that the change we need?" Mulcair said of Trudeau in the speech, which also contained the NDP's standard criticism of Harper's decade in power.

"How can Canadians trust a person who so easily abandons one principle for another?"

Mulcair delivered the address to hundreds of chanting supporters on a day the NDP unveiled its campaign plane.

All three major parties now have their official planes and the pace of the campaign is expected to accelerate. The parties expect more and more Canadians to tune in following the Labour Day long weekend, which unofficially marked the end of vacation season.

With the new leg of the race underway, the clash between the NDP and Liberals began to intensify Tuesday.

Before the Toronto rally, the Liberals distributed their own list of criticisms directed at Mulcair.

Toronto Liberal incumbent Chrystia Freeland released a statement containing warnings about several of Mulcair's promises, including his plan to create one million $15-a-day child-care spaces. That program would eventually cost $5 billion annually once fully implemented in eight years.

Freeland said the program would saddle provinces with billions of dollars in costs.

She also challenged Mulcair's minimum-wage pledge, arguing it would only help less than one per cent of minimum-wage earners.

"Tom Mulcair will say whatever people want to hear," Freeland said in the statement, which also underlined the NDP-Liberal fight for the centre-left.

"Mulcair isn't the progressive alternative to Harper he's pretending to be."

Earlier Tuesday, Mulcair stopped in another important area for the NDP: Montreal.

At the city's Pierre Elliott Trudeau airport, Mulcair demurred on revealing costing details of his program, which contains several pricey commitments.

He said he would reveal all the revenue sources and costs in due course -- and only after the NDP announces a few more promises.

"None of the major parties has yet provided their full accounting, but of course the NDP will be doing that," said Mulcair.

"You can be sure that we're going to produce exact accounting on all the numbers in our platform."

The New Democrats have promised to balance the books next year if they win power. But that pledge has come under attack from rivals, who argue a weakened economy will force the NDP to achieve it by hiking taxes and cutting services.

Mulcair reiterated that the NDP would pay for its commitments in part by cancelling the Conservatives' $2-billion-a-year income-splitting measure for families with kids and by raising corporate tax rates -- though he has yet to specify by how much. He has also announced he would close a tax loophole on CEO stock options.

While in Montreal, Mulcair promised to help the aerospace industry, a sector that has seen hundreds of layoffs this year.

He said he would set up a $160-million, four-year fund to help small- and medium-sized aerospace companies adopt new technology and increase production. The plan would require firms to show how they would create jobs and provide professional training to workers.

Mulcair also committed to $40 million over four years for the Canadian Space Agency's development program to help companies commercialize new space technologies, and said he would lead trade delegations to help promote the industry.

Montreal Liberal incumbent Marc Garneau, a former astronaut, warned Tuesday that the NDP plan to increase corporate tax rates would hurt the aerospace sector and manufacturers.