Liberal Leader Justin Trudeau is hinting he'd repeal the Conservatives' controversial prostitution legislation, as he and NDP Leader Thomas Mulcair vie to be the favoured alternative to Prime Minister Stephen Harper in an election scheduled for later this year.

With Mr. Mulcair offering policy prescriptions such as a national child-care program, Mr. Trudeau is taking aim at Mr. Harper's record, including the prostitution bill and the government's income-splitting plan, which will reduce the tax burden on families with stay-at-home parents.

The Liberal Leader is not planning to release specifics on what policies a Liberal government would pursue until a campaign is launched, which is expected in mid-September for an October vote, though the Prime Minister can call it earlier.

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In an interview aired Sunday, Mr. Trudeau said the Conservatives are motivated by ideology on issues such as prostitution while he favours an "evidence-based approach," which, he says, is why he is promoting legalization of marijuana and controlling access to the drug.

"On prostitution, we need to make sure we're basing our decisions on evidence," he told CTV's Question Period. "The Supreme Court has said the framework that existed was not protecting vulnerable people and women from violence and that is the lens we need to look through as we move forward on this difficult issue."

Ontario's Liberal Premier Kathleen Wynne has asked the provincial Attorney-General to launch a review of the constitutionality of the new federal law, which was adopted in response to the Supreme Court's rejection of the previous prostitution statute. Critics say the recently enacted law puts sex workers in even greater danger.

Year-end polling showed Mr. Trudeau's Liberals running neck-and-neck with Mr. Harper's Conservatives, while the strength of Mr. Mulcair's NDP is centred in Quebec.

Pollster Nik Nanos said the young Liberal Leader needs to highlight a solid team and potential cabinet to persuade Canadians that he is ready to govern, while Mr. Mulcair needs to break out of Quebec and shed his image as merely an effective Opposition leader.

"Mr. Harper needs a little co-operation from both opposition leaders," Mr. Nanos said in an interview Sunday. "For Tom Mulcair, he needs him to perform well in order to split votes in the 905 [area of Toronto's suburbs] and other swing areas. And for the Liberals, he needs them to make a mistake."

Mr. Trudeau said he is ready to take on the Prime Minister over economic issues, as the Conservatives launch attack ads that question his judgment on fiscal matters.

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"In terms of reckless spending decisions, it would be hard to find a better example than [Mr. Harper's] ill-thought-out income-splitting proposal, which talks about taking $2.4-billion – the large part of the surplus that hard-working Canadians sacrificed to create – and giving it to the 15 per cent of wealthiest Canadians," Mr. Trudeau said.

As for Mr. Mulcair, he is looking to "relaunch" his effort to establish some momentum with promises such as increases to the federal minimum wage to $15 an hour, a national daycare program and opposition to corporate tax cuts and pipelines such as the Keystone XL project, which Mr. Trudeau has favoured.

The NDP Leader appeared with his wife, Catherine Mulcair, on the CTV program as he tried to soften his hard-nosed image and broaden his appeal. He acknowledged that effort was knocked off track last fall, first by the Parliament Hill shooting, which put a focus on security issues, and then by the sexual-harassment controversy in which Mr. Trudeau suspended two male Liberal MPs from caucus after allegations involving two NDP women MPs.

"Both of those issues were very important – you couldn't not cover them," he said. "But it's only in January that you're going to see the beginning of the election year of 2015, with a final date of October 19. It's going to be a long campaign."