Though polls in the run-up to the June 12 election have suggested varying outcomes in terms of a Liberal or Tory government, a minority or a majority government, the New Democrats seem to remain in third place.
That leaves more than usual at stake for all of the leaders, said Jonathan Malloy, the chairman of Carleton University's political science department.
"Debates offer a chance to change things up but usually don't, so they tend to be overhyped," Malloy said. "But because of the vulnerability of both major parties in the polls and lack of strong momentum, (the debate) could attract more attention since there seem to be a lot of undecided or volatile voters out there."
Expect to see Liberal Premier Kathleen Wynne and Progressive Conservative Leader Tim Hudak largely focus on each other in the debate, he said.
In the "two-horse race," those two leaders will likely be front and centre in the debate, but Horwath shouldn't be discounted, said Western University politics professor Cameron Anderson.
"The outcome is still very much in doubt," he said. "I think that it perhaps focuses the efforts of the two leaders, Ms. Wynne and Mr. Hudak, in terms of one another, but...I do think that Wynne needs to be considerate of her left flank as well and argue both ways."
Hudak's main task in the debate will be to defend his maligned "Million Jobs Plan," Anderson said.
"I think he needs to have a ready and defensible response to any sorts of criticism that may emerge," he said.
Hudak has come under repeated fire from economists and his political opponents for promised public-sector job cuts even as he pledged to create one million jobs over eight years.
The consensus among experts appears to be that his pledge is based on faulty math — something Hudak denies.
Wynne and Horwath will try to turn Hudak "into a human pinata," pushing him to explain the numbers behind his plan, said Ryerson University politics professor Wayne Petrozzi.
"It's really the only opportunity for the other two to draw him out and for him it's also very important — it's the one time he's not going to be able to control the narrative," Petrozzi said.
"His job primarily is he's going to try to simply dismiss these criticisms as, 'You're a pessimist. I'm an optimist. I'm a good times guy. Turn the page, Ontario. Vote for a sunny day.'"
Wynne will have to defend the Liberal record, which will certainly include barbs from the other two leaders about the cancellation of two gas plants three years ago that could end up costing taxpayers more than $1 billion.
"I think that she needs to, as much as possible, focus on the future," Anderson said. "She's very good at using the notion of government as, she uses the phrase, a force for good and putting forward a very positive impression of government and its role in the province."
Wynne, the only leader who hasn't participated in the televised debate before, said Monday that the event is an "important juncture" in a campaign and an opportunity for her to talk to voters about her plan.
"The fact is there are a lot of people who wait for the debate to actually tune in to an election campaign. So a lot of them, because of the busyness of their lives, they haven't necessarily gotten all the issue and they'll be looking tomorrow night for some clarity," she said.
"Is there pressure? Absolutely. But there's pressure because this is such an important election. It's such an important election and there's such a stark choice between what Tim Hudak is proposing for the province, which I really believe would take us backwards, and what we're proposing, which will take us forward."
Meanwhile, Hudak predicted his opponents would try to sway voters with empty promises, and said he'll stand out by being straightforward about his plans.
"I think they'll see somebody in me, standing there and being honest, being direct and being crystal clear about where he stands — less waste, more jobs in the private sector, lower taxes, more affordable energy," he said. "Nothing exciting, not a great actor, straight up."
The NDP's Horwath said she was looking forward to sparring with her political opponents.
"This campaign has been all about specific ideas, it's been about waste and corruption versus nonsensical ideas versus a practical plan that makes sense and addresses people's priorities," she said.
"It's not all that difficult to prepare when you've seen what's been happening here in this province and when you've listened to the people of this province."
Unlike Wynne and Hudak, Horwath must adopt strategies on multiple fronts, the experts said.
"It's clear that in Ontario, at least, Liberals and New Democratic voters are far more likely to switch than Conservative voters," Petrozzi said.
"(Horwath) is going to have to stop what's happening currently, bleeding New Democratic voters into the Liberal column. So she's going to have to find a way after dispensing with Mr. Hudak, to speak to prospective NDP voters, which include some Liberals, that in fact she is worth their vote."
Horwath will also be put on the defensive as to why she triggered the election after refusing to support an NDP-friendly budget, Anderson said.
"Her big problem as the campaign has emerged is really: what is the NDP standing for?" he said.
"I think she needs to be able to continue to focus on the Liberals as not trustworthy."
Horwath may also have to speak specifically to her base, given concern expressed by party stalwarts threatening to withdraw their support over what they see as a shift to the right by the party, Anderson said.
In a recent letter to Horwath, which was obtained by the media, 34 long-time supporters wrote they were "seriously considering" not voting for the NDP on June 12.
But it's not just about what the leaders say in the debate, it's how they say it, the professors said.
"There's a lot of literature in political science that would suggest that leadership matters and that personal characteristics of, and the perceptions of those characteristics, of the leaders matter, things like honesty or trustworthiness or character," Anderson said.
In that, Hudak faces perhaps the steepest challenge, Petrozzi said.
"He seems to at times almost ooze discomfort," he said. "It's as if he looks at that thing, those cameras staring at him, and he imagines they're rifles."
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