Tonight's election debate between Ontario's major party leaders could make or break their campaigns, according to experts following the race. Voters will be keeping a close eye on leadership styles, not just on the substance of what the party leaders say.

Liberal Leader Dalton McGuinty, Progressive Conservative Leader John Tory, and NDP leader Howard Hampton will face off at 6:30 p.m., live on CTV News after the evening newscast.

The leaders' debate will be the only such event before the Oct. 10 election. So, it could help shape the ultimate outcome of the race.

Cameron Anderson, a political scientist at the University of Western Ontario, told CTV.ca that voters will be keeping a close eye on leadership styles, not just on the substance of what the party leaders say.

He says that it may not be fair to judge a candidate based solely on a single debate, but there is ample evidence to suggest that a good or poor performance by a leader can turn the tide of an election campaign.

"Voters want to know, 'Can I trust this person to lead the province?'" says Anderson.

He says that many voters make judgments about a candidate's abilities, integrity, and overall gravitas, based on what they see during debates.

McGuinty will want to avoid being tagged as a leader who breaks promises, says Robert Drummond, the dean of the Faculty of Arts at York University. He will have to convince voters he did his best to keep his word when it comes to assurances he made during the last provincial election. Drummond adds that McGuinty also needs to explain why some promises weren't kept.

Drummond says that Tory will have to distance himself from the Mike Harris years. Harris, who led the Conservatives as premier from 1995 to 2002, made sharp cuts to the province's public sector. Drummond argues if the Conservatives want tax cuts, they'll have to convince debate-watchers that they won't slash services.

But Drummond noted that Tory could face an uphill battle with voters if he pushes his party's position to provide public funding for all religious schools. Currently, only Roman Catholic schools receive public funds due to constitutional reasons.

"This issue may get the most heat, if not the most light," says Drummond.

He says that the private schools issue is controversial and will receive lots of media attention, but it will likely not convince voters one way or the other. He added that most voters have already made up their minds about the issue and won't likely be swayed by what is said during the debate.

According to Anderson, Tory has so far failed to adequately explain why his party supports public funding for religious schools in general and not just Catholic schools. The latest CTV-Globe and Mail poll indicates 71 per cent of Ontario voters oppose public funding of faith-based schools. The debate may offer Tory a chance to explain his position better, but Anderson added that it may be a tough sell.

"The Liberals and NDP may be wise to poke at this issue," says Anderson.

The NDP also should use the debate to show voters that a vote for their party "isn't a wasted vote," says Drummond.

He added that despite the fact that the Green Party will not be allowed to participate in the debate, they could still come out a winner.

"(The debate) will hurt them because they're not visible, but it could also help because people may say 'that's not fair.'"

The Green Party, which will be shut out of the debate because it does not have a sitting member in the legislature, told CTV.ca that it will hold a debate of its own. Party leader Frank de Jong, along with supporters, will watch the event at a Toronto hotel and provide his own answers to issues that are raised. The event will be broadcast on the Internet.

Drummond says the Green Party may gain some sympathy because they have quite a bit of popular support in the polls, despite not having any elected members. The latest CTV poll shows that the Greens have 10 per cent voter support.

The poll puts the Liberals in first place with 40 per cent support from decided voters. The Conservatives are in second place with 34 per cent, and the NDP is in third with 16 per cent.