Ontario Liberal Leader Dalton McGuinty has ruled out a coalition in the event no party wins a majority in Thursday's election.

In a letter obtained by The Canadian Press on Sunday, the premier tells Progressive Conservative Leader Tim Hudak that he won't be making any deals to form a government.

"I am running to form a Liberal government — and only a Liberal government," McGuinty said in the letter. "There will be no coalition with either your party or the NDP."

The latest polls indicate the Liberals and the Progressive Conservatives in a dead heat, raising the prospect of a minority government in Ontario for the first time in 26 years, with the NDP under Andrea Horwath as kingmaker.

In his letter to Hudak, McGuinty said his opponents are using talk of a minority government as political ammunition.

Hudak suspects 'backroom deals'

"Over the course of the weekend, you and Ms. Horwath have turned away from promoting your individual platforms and have engaged instead in trying to leverage political advantage through minority government speculation," McGuinty said.

Conservative Leader Tim Hudak says if no party wins a majority on Thursday, the Liberals and New Democrats might form a coalition and raise taxes. CBC

Hudak has been accusing McGuinty of planning "backroom deals" with the New Democrats.

Earlier Sunday, he warned that Ontario could end up with a minority government coalition in which the Liberals and NDP would work together to hike taxes.

"The Liberals and the NDP: they'll increase taxes and they'll spend money on everything under the sun," Hudak said at a campaign stop Sunday.

When asked if he would work with the New Democrats if they dropped a plan to raise the corporate tax rate, Hudak indicated he wasn't interested.

"I'm in this election to win and bring change, not play 'Let's Make a Deal'," Hudak said, suggesting the Liberals and NDP would cook up a deal.

Liberals see opponents as 'desperate'

The Liberals said McGuinty addressed his letter only to Hudak because of the Tory leader's comments.

However, a Liberal source attacked both the Conservatives and NDP over minority talk, saying it seemed they were "getting increasingly desperate."

NDP Leader Andrea Horwath hasn't ruled out the possibility of a coalition but says Ontario voters should have their say first. Adrian Wyld/Canadian Press

Hudak's strategy is reminiscent of Prime Minister Stephen Harper's, whose spring election included frequent warnings that the federal Liberals and NDP would scheme to form a coalition if his Conservatives did not get a majority.

McGuinty said voting Liberal would be the only way to ensure the "strong, stable, positive government" Ontario needs in uncertain times.

Campaigning in Toronto, Horwath side-stepped speculation about a minority government, focusing instead on what the NDP would do during its first 100 days in office.

While Horwath did not dismiss the possibility of a coalition, she spent the final Sunday of the campaign focused on her bid to become premier.

Horwath stresses 5 priorities

"My job is to continue to let Ontarians know what my commitments are — which is why I put those commitments out clearly today — so that they know exactly what they're going to get in the first 100 days," she said after a raucous downtown rally.

"The very least they deserve is not focusing on ourselves and on what our power might be, but focusing on what we should be focusing on all along, and that is how we're going to fix this province."

Horwath said her priorities for her first 100 days would be job creation, pocketbook relief, strengthening health care, helping Ontarians make "affordable" green choices, and raising corporate taxes.