MONTREAL -- A fiery Justin Trudeau told a Liberal Party convention Saturday that Stephen Harper practices the politics of division, much in the same way as Pauline Marois, a reference to the PQ’s Charter of Values project.

A representative of Marois later lashed back against the description in an email.

“One of the worst acts of Canadian history was made by the government to which Trudeau is the heir,” wrote PQ MNA Alexandre Cloutier. “That’s the imposition of the constitution in 1982, done without the consent of Quebec.”

Trudeau's impassioned speech before 3,000 delegates was long on values, dotted with partisan jabs but short on details about the kinds of policies he'd implement.

Apart from a vow not to increase taxes on the already struggling middle class whom Trudeau has promised to champion, he laid out only the broadest of economic agendas.

The watchword appeared to be balance: activist but not intrusive government, strategic investments to spur economic growth but not wanton big spending.

"Too much government is an enemy of freedom and opportunity, but so to is too little," he told party faithful.

"Governments can't do everything, nor should they try. But the things it does, it must do well."

Trudeau once won a charity boxing match against Patrick Brazeau, one of three formerly Conservative senators now under suspension from the Senate for making allegedly improper expense claims. For all his promises to stay on the high road, Trudeau showed Saturday that he can still pack a good punch.

He turned the tables on Prime Minister Stephen Harper, whose Conservatives have relentlessly attacked Trudeau for not having the judgment to be prime minister.

"Anyone who put Pamela Wallin, Mike Duffy and Pat Brazeau in the Senate might want to be careful about making judgment a campaign issue," Trudeau said to hoots of laughter.

He accused both Harper and NDP Leader Tom Mulcair of exploiting Canadians' anger over the Senate expenses scandal to make "cynical, dangerous" promises to either turn the upper house into an elected chamber or to abolish it altogether -- either of which would require re-opening the Constitution.

"They are willing to play games with the Canadian Constitution for narrow partisan advantage," Trudeau said.

"Now, Mr. Mulcair and Mr. Harper may think so but I disagree. Mike Duffy is not worth another Meech Lake," he said, referring to the 1990 constitutional accord whose ultimate failure almost fractured the country.

Rather than contemplate another round of constitutional bickering, Trudeau said Liberals will stay focused on resolving the challenges facing middle class Canadians.

His speech was long on diagnosing the economic problems of a fictional "Nathalie," a young mother whom he described as worried about her kids future, her family's debt load, whether she'll ever be able to afford to retire.

While he offered no specific prescriptions for her woes, Trudeau said government should be investing strategically in things like post-secondary education and infrastructure to spur economic growth.

That said, he added: "We need to ensure that governments keep costs as low as possible, especially for middle class households. The middle class is already having a hard time making ends meet and struggling with debt. Tax increases for them are not in the cards and not on the table."

He described his vision of a strong economy as one that "makes sure every Canadian has a real and fair chance at success."

And he harkened back to the "just society" his late father, Pierre Trudeau pledged to create when he became prime minister almost 50 years ago, in urging Liberals to help him build a party that will stay committed to the principles of "fairness, freedom, progress, opportunity, compassion."

Trudeau also used the speech to attempt a little poaching from Harper's Conservative base, advising Liberals to reach out to Tory voters who are fed up with the Harper government.

"The 5.8 million Canadians who voted Conservative aren't your enemies. They're your neighbours. These are good people," who've been let down by Harper, he said.

And in a direct message to grassroots Conservatives, Trudeau said: "We might disagree about a great many things but I know we can agree on this: Negativity cannot be this country's lifeblood."

-with files from The Canadian Press