The latest Harris-Decima poll, conducted for The Canadian Press, asked respondents whether they would support joint Liberal-NDP candidates in their own ridings, a cornerstone of would-be leader Nathan Cullen's campaign.
Overall, 37 per cent of those surveyed said they would support such a candidate, while 23 per cent said they would support the Conservative candidate in such a scenario.
One in five respondents said they would support a different candidate; 21 per cent of those surveyed did not offer an opinion.
Nationally, 41 per cent of respondents who offered an opinion identified Mulcair as the best choice for NDP leader, followed by 13 per cent for rival Peggy Nash, 10 per cent for Paul Dewar and eight per cent for Brian Topp.
However, support for Mulcair — a Montreal MP — is overwhelming in Quebec, but decidedly more mixed in the rest of the country.
Among Quebec respondents, 77 per cent with an opinion tapped Mulcair as their preferred choice, with all of his rivals in the single digits. Outside Quebec was a different story: 24 per cent preferred Mulcair, compared with 18 per cent for Nash, 13 per cent for Dewar and 11 per cent for Topp.
"Our survey results suggest that while Thomas Mulcair is the consensus choice for best leader, outside of Quebec, opinion is much more divided," said Harris-Decima senior vice-president Doug Anderson.
Overall, 56 per cent of those surveyed outside Quebec said they didn't know who would make the best leader of the NDP. Among those in Quebec, 39 per cent said they didn't know who they'd pick.
It's Mulcair's cachet in Quebec that has propelled him into the lead of the NDP leadership race. Once a western-based protest party, the NDP's world has revolved around Quebec since last May's election, when an orange wave swept the province and vaulted the party into official Opposition status for the first time in its 50-year history.
Harris-Decima's omnibus telephone poll surveyed just over 1,000 Canadians March 15-19 and is considered accurate within plus or minus 3.1 percentage points, 19 times in 20.
Cullen has made the idea of joint candidates — allowing local New Democrats and Liberals in Tory-held ridings to decide whether to run a single candidate — a cornerstone of his leadership campaign.
Initially, the proposal was considered toxic to Cullen's chances. But his campaign has taken off in the late stages of the race, propelled in part by online advocacy organizations which maintain co-operation among progressive parties is the best way to ensure defeat of Stephen Harper's Conservatives.
Interestingly, the survey suggests it's Liberal voters who would be most likely to support a joint candidate. Nearly one-third of those NDP supporters surveyed said they would take their vote elsewhere.
Three out of four respondents who identified themselves as Liberals said they would vote for the joint candidate, compared with 58 per cent of New Democrats, 37 per cent of Green supporters and 18 per cent of Bloc Quebecois supporters.
The poll suggests the idea has some currency with voters, Anderson said.
"Recognizing that the devil will almost certainly be in the details, the notion ... appears to have some basic degree of attraction for some Canadian voters," Anderson said.
"Our question forced Canadian voters to assume that a joint NDP-Liberal candidate would end up being offered in their own riding. Within that context, more Canadians claim they would vote for that joint NDP-Liberal candidate than for any other party’s candidate."
The poll results suggest a joint NDP-Liberal candidate would be most popular in Quebec and Atlantic Canada, while the Conservatives would continue to be the preferred choice on the Prairies.
"The level of support for a joint NDP-Liberal candidate is not simply a sum of the support for each of the two parties," Anderson said.
"The results also show that not all partisan supporters react in similar or predictable ways."