NDP leadership hopeful Brian Topp has a warning for his rivals as the party prepares to pick a new boss: don't be boring.

Topp suggested that if he and the other seven candidates can't find good issues to debate over the course of their leadership contest, Canadians will tune out and the party will suffer in the next election.

"If New Democrats are going to win, we can't be boring," Topp told CTV's National Affairs from Montreal on Monday. "We need to find some issues to debate."

Perhaps that's why Topp attacked his chief rival, Montreal MP Thomas Mulcair, last week and accused him of being a liability in Quebec -- the province where the party made the most gains during the last election.

And while there are several other candidates in the NDP leadership contest, the vote on March 24 could very well come down to what separates Topp from Mulcair.

While both men started out in provincial politics, they did so with different parties: Topp worked with the New Democrats in Saskatchewan and Mulcair worked under Jean Charest with the Quebec Liberals.

Topp is drawing particular attention to Mulcair's Liberal past.

"There are some interesting distinctions between us, and I think they're worth discussing," said Topp, who claims that his rival wants to push the party away from its socialist roots and towards the centre.

"I worked for an NDP provincial government that talks about big dreams (and) about getting there a practical step at a time. Mr. Mulcair was an architect and was at the centre of a Liberal government in Quebec that's from a different tradition."

"He said pretty clearly ‘I think that the party should move to the centre, more to the right,' and I don't agree."

"It's a pretty fundamental issue of where we want to go with our party," Topp said.

Niki Ashton, Nathan Cullen, Paul Dewar, Peggy Nash, Romeo Saganash and Martin Singh are also in the race.

Topp has said he would increase taxes and get rid of proposed corporate tax cuts -- a move that would firm up the party's leftist base, but could ultimately cost them centrist voters.

But Topp said that he isn't worried about alienating voters in the middle of the political spectrum.

"I think those proposals are the only practical way, not only to win power, but to do something after you win it."

"The Conservative playbook has gone far enough," he said.

Meanwhile, Mulcair has won growing endorsements from many high-profile New Democrats since launching his candidacy last year.

He has also increased the party's membership in Quebec, with a goal of boosting the province's membership to 20,000 -- a goal that would boost his performance at the leadership convention.

Mulcair has also publicly mused about taking the "high road" during the race.