The Conservatives lead the Liberals by more than eight percentage points in the polls as Prime Minister Stephen Harper prepares to square off against his opponents in the English-language leaders' debate on Tuesday night.

A poll released Monday puts the Conservatives in the lead with 39.7 per cent support from surveyed voters, with the Liberals trailing behind at 31.2 per cent and the NDP at 16.8 per cent. The Bloc Quebecois received 7.8 per cent support from respondents, while the Greens had 4.0 per cent.

The Nanos Research poll conducted for CTV and The Globe and Mail also found that 52.6 per cent of the surveyed voters believe policy will play a key part in their decision on Election Day. That means that the Tuesday night debate will provide leaders with an opportunity to target voters who are looking for more information about their party platforms.

Pollster Nik Nanos said debates have the potential to push a party up or down in the polls, as voters can form a strong impression about the way the leaders stack up against one another.

"The debates are key junctures in the campaign because many Canadians tune in earnest to size out and check out all of the federal party leaders," Nanos told CTV News Channel from Ottawa on Tuesday morning.

"But realistically, it's about two things: exceeding expectations and not making mistakes."

The end goal for Harper will be to try to hold onto the Conservative support he has, while Liberal Leader Michael Ignatieff and NDP Leader Jack Layton will be trying to paint themselves as a better choice for voters.

Nanos said the Conservative leader will have to confront the issue of a still-unreleased auditor general report that has raised questions about the way Ottawa handled a $50-million infrastructure fund during the 2010 G8 summit.

The Tories say the contents of the final report are very different than a draft version that was leaked to media on Monday.

"We can't underestimate the credibility that the auditor general of Canada has," Nanos said.

"You know when she says something, people listen. And I think it's going to be a key vulnerability for Stephen Harper tonight, he's going to need a very clear answer and I'm sure Michael Ignatieff and Jack Layton and Gilles Duceppe are going to be on the offensive and be very aggressive on this particular issue."

Watch live coverage right here on CTV.ca leading up to the leaders' debate, starting tonight at 5 p.m. ET / 2 p.m. PT.

The provincial picture

The Nanos poll suggests the Tories and Liberals are neck and neck in Atlantic Canada, Quebec and Ontario. The New Democrats trail these parties by more than 20 percentage points in Ontario and Atlantic Canada, but sit within three percentage points of the Liberals and six percentage points of the Tories in Quebec.

In Western Canada, the Conservatives continue to hold a significant advantage over their opponents, with support from 51.2 per cent of decided voters in Alberta and 45.1 per cent in British Columbia.

Monday's Nanos Research poll is based on a telephone sample of 990 decided Canadian voters, surveyed between April 9 and April 11. It is considered accurate to within 3.1 percentage points, 19 times out of 20.