WATCH ABOVE: Stephen Harper says a majority of Canadians agree with his opposition to legalizing marijuana

With the curtain about to rise on the climactic second act of the Mike Duffy trial, Justin Trudeau promised Tuesday to clean up the scandal-tainted Senate, while Stephen Harper set his sights on neighbourhood drug labs.

The Liberal leader vowed to clean up the prime minister’s “mess,” accusing Harper of leading the “most secretive, divisive and hyper-partisan government in Canada’s history.”

That mess, of course, is the Senate, and in particular Duffy’s trial, which was scheduled to enter its most explosive phase Wednesday with none other than Nigel Wright, Harper’s former chief of staff, as the first witness.

Reality Check: What’s the evidence behind Harper’s anti-drug strategy?

Wright, Harper’s former chief of staff, is the man who provided Duffy with $90,000 of his own money to repay his disallowed housing and travel expenses. The former Conservative senator has pleaded not guilty to 31 charges including fraud, bribery and breach of trust.

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Trudeau, determined to keep the Conservative scandal top of mind for Canadians, spoke Tuesday of transparency, saying it would be a fundamental principle in a Liberal government.

He also promised to bring in a merit-based appointment process to the Senate.

Harper, meanwhile, tried to avoid being drawn back into the Duffy fray with yet another policy announcement – his fifth with the 11-week campaign still in its infancy – before travelling to B.C. and later northern Canada.

READ MORE: 5 things to know before Nigel Wright testifies at Mike Duffy trial

Harper promised a 20-per-cent increase in funding – to almost $27 million a year – to help the RCMP target marijuana grow-ops and meth labs and another $500,000 a year over four years on a national toll-free hotline for parents to get information about drug use among the country’s youth.

And he took the opportunity to score some points on Trudeau, who has already pledged his support for legalizing marijuana.

WATCH: PM Harper announces plan to strengthen anti-drug strategy

In jurisdictions where marijuana is legal, such as parts of the U.S. and Europe, the drug becomes “more readily available to children, more people become addicted,” and there is a decline in health outcomes, Harper said.

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“We just think that’s the wrong direction for society and I don’t think that’s the way most Canadians want to deal with this particular problem.” Tweet This

NDP Leader Tom Mulcair, however, was more interested in Harper’s travel itinerary, in particular the fact he was getting as geographically far away from Ottawa as possible.

“I do find it interesting that Mr. Harper has decided to try to hide out in the North Pole during the Mike Duffy trial this week,” Mulcair said.

“On a whole series of subjects, Mr. Harper has said one thing and its opposite in the Mike Duffy affair. You can’t say one thing and then its opposite and have them both be true. A lot of that is going to be catching up with Mr. Harper this week. He can run but he can’t hide.”

READ MORE: Leaders’ debate, attack ads and a week of campaigning have little effect on voters, Ipsos poll shows

Mulcair later confirmed he would participate in a bilingual Munk Debate on foreign affairs, after having said he would only be there if Harper was and if there would be an equal number of debates in both official languages.

Confusion, however, continued to reign Tuesday. The Conservatives have agreed to participate, and while the Liberals have said they would be there on Sept. 28, they have yet to confirm their attendance.

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Green party Leader Elizabeth May was not invited.

While campaigning in Quebec, a province the NDP dominated in 2011, Mulcair got some welcome news: one of the province’s largest and sovereigntist-leaning labour federations has dropped its long-standing endorsement of the Bloc Quebecois and some of its member unions are supporting the New Democrats.

Mulcair said he will “work hard to maintain the support” of unions in Quebec in order to “expand our traditional base and rally progressives across Quebec and Canada.”

The Quebec Federation of Labour, also known as the FTQ, covers 37 labour unions and counts 600,000 members.

The NDP offers a big tent to Quebecers, even those who supported separatism in the past, Mulcair said.