A relatively tame final Liberal leadership debate saw virtually no sparring between candidates except on the issue of electoral reform.

Montreal MP and perceived frontrunner Justin Trudeau and Vancouver MP Joyce Murray faced off on the issue of strategic voting -- in particular, co-operating with opposition parties to effectively end vote-splitting.

Trudeau attacked Murray’s proposal to run candidates against each other in the “progressive parties” so only one progressive candidate is on the ballot. Trudeau said it will lead to NDP Leader Thomas Mulcair “as prime minister and that’s not what I’m interested in.”

 “I’m very worried that if we assemble a hodgepodge coalition or coming together or co-operation that actually removes choices from Canadians by forcing them to make an either-or-choice, they will not believe we’re ready to govern,” he said during the debate held in Montreal.

Murray said it shifts Canada into a “new style” of electoral reform that is more co-operative.

“It’s transparent, it’s democratic,” she said.  

The debate on vote-splitting was touched off by Green Party Leader Elizabeth May’s announcement Saturday that she won’t run a candidate in the upcomingLabrador byelectionto fill the seat left vacant by Conservative MP Peter Penashue.

The cabinet minister resigned this month over spending irregularities in his 2011 election campaign. He admitted that his campaign accepted illegal donations, but said he was unaware of them at the time and blamed the mistakes on an “inexperienced volunteer” -- his former official agent.

Murray said in a news release that she asked the Green Party leader not to run a candidate in the byelection.

Down to six following Marc Garneau’s and David Bertschi’s departures from the leadership race, contenders also spoke on the issues of the environment, the justice system, and promoting Canada on the world stage. 

Other contenders include Martin Cauchon, Martha Hall Findlay, Deborah Coyne, and Karen McCrimmon.

University of Toronto political science professor Chris Cochrane told CTV’s News Channel that there was limited opportunity in the final debate for contenders to challenge Trudeau.

Cochrane said there seemed to be a hesitance among hopefuls to attack Trudeau directly.

“You do see a lot of alluding to the fact that maybe there’s no substance there,” Cochrane said, noting that Cauchon and Hall Findlay pressed Trudeau to reveal his specific platform on Quebec relations and his targets for post-secondary education, respectively.

“I think there’s a real sense within the party and among the other candidates that he’s light on specifics and not really much opportunity to push him to reveal what those are.”

As the race enters its final weeks, there is a continued sense that  contenders cannot compete with Trudeau.  

After the debate, Coyne said she knows she won’t win the race, but remains in it to shed light on her ideas.

Liberals will choose a new leader during a leadership convention scheduled for April 14.

With a report from CTV’s Daniele Hamamdjian