Once an odds-on favourite to win a second term as mayor, Denis Coderre finds himself tied with Valérie Plante in a new poll released today, less than a week before Montreal's municipal election.

The CROP poll, commissioned by Radio-Canada, found 39 per cent of Montrealers back the Projet Montréal leader, compared with 37 who support Coderre. An additional 17 per cent of respondents were undecided about their choice for mayor.

The poll was conducted between Oct. 19 and 24 — a period covering the campaign's two debates — and surveyed 1,094 Montreal voters over the internet.

Polls this size usually have margins of error around three percentage points, meaning the level of support for Plante could be as high as 42 per cent or as low as 36 per cent.

But even so, that the campaign is this close, at this late stage, runs contrary to what many expected at the outset.

"It's quite surprising. We thought Mr. Coderre would have had a lead in this campaign, and they're neck-and-neck," said CROP's president, Alain Giguère.

"Coderre began this race thinking and communicating to everyone that it was obvious he was going to win."

According to Giguère, the biggest issue propelling Plante's surge is construction and the resulting congestion on Montreal roads.

That was the most important issue for 83 per cent of respondents, higher than snow removal (80 per cent) and public transit (79 per cent). The poll suggests 54 per cent of Montrealers trust Plante to improve their traffic woes, while 45 per cent felt the same way about Coderre.

"She's been hammering this for the past month and she's been credible in saying to Montrealers that she would be capable of doing a way better job than Mr. Coderre," Giguère said.

"That's the big weakness of Mr. Coderre."

The poll also indicates that Montrealers, by a wide margin, are favourable to Plante's proposal to build a new Metro line linking Montreal North with Lachine.

But while 47 per cent back the idea despite the cost, 43 per cent support it only in theory and agreed with the statement that the so-called Pink line is not "financially realistic."

Coderre's personality problems

The closeness of the race is all the more surprising given that Montrealers appear content, overall, with Coderre's handling of the city.

Conventional political wisdom dictates that a sense of dissatisfaction needs to be widespread for an incumbent's re-election to be in jeopardy.

But of those polled, 58 per cent said the city improved to some degree over the past four years, and 55 per cent gave Coderre good marks for leadership.

His other personality traits, though, could be weighing him down. Plante scored better than him on measures of integrity, willingness to listen and she is seen as more inspirational.

Only 17 per cent of respondents said they found Plante arrogant while 55 per cent endorsed that description of Coderre.

So how to reconcile the dislike for Coderre with the appreciation expressed for the job he has done?

It is possible, said Giguère, that Montrealers found his strong personality well-suited to the particular situation the city was in four years ago, but that priorities have since shifted.

The 2013 election was prefaced by the resignations of mayors Gérald Tremblay and Michael Applebaum, amid an escalating series of corruption scandals.

"The city was perceived as needing to be rebuilt and [Coderre] is perceived as having done the job," Giguère said.

"But today we've moved into a new mood in which we don't feel as though we need to rebuild the city as much. Maybe we need to be listened to and Plante seems to incarnate that kind of leadership."

Challenges of polling at the municipal level

With 1,094 respondents, the CROP poll has the largest sample size of those published to date in the Montreal campaign.

Its findings, moreover, align with the earlier polls — last week's Leger poll commissioned by Projet Montréal and a Mainstreet poll from early in the campaign — which also pointed to a narrow race.

But polling at the municipal level has an uneven record in terms of predicting electoral outcomes. Alberta's polling industry, and Mainstreet in particular, entered a state of deep self-reflection following Calgary's mayoral election earlier this month.

Mainstreet published a series of polls forecasting a landslide victory for challenger Bill Smith, only for incumbent Naheed Nenshi to win by seven points.

One of the biggest difficulties of polling at the municipal level is accurately anticipating voter turnout, which tends to be much lower compared to provincial and federal elections (Montreal's was 43 per cent in 2013).

Respondents are notoriously unreliable when it comes to telling pollsters whether they will head to the polls on voting day, which skews their predictive value.

This is where a silver lining exists for the Coderre camp. Their candidate scored better among older Montrealers, who are traditionally more likely to vote.

Plante, on the other hand, did better among the younger set, but they have turned out in fewer numbers in past elections.

Polls will be open from 10 a.m. to 8 p.m. on Sunday.

Make a date with CBC for election night this Sunday, Nov. 5:

Online: Get breaking news and live results at cbc.ca/montreal after polls close at 8 p.m.

On Facebook: Join host Debra Arbec for a 90-minute Facebook Live starting at 10 p.m. with results, analysis and reports from across Quebec.

On TV: Watch our live results show at 11-11:30 p.m. on CBC Television.

On Radio: Listen to CBC Radio One starting at 8 p.m. for a province-wide show hosted by Mike Finnerty in Montreal and Susan Campbell in Quebec City.