Polls have opened in two Ontario by-elections that could give Premier Dalton McGuinty's Liberals the majority government they were denied last October.

The Liberals are expected to hold on to the Vaughan riding vacated by former finance minister Greg Sorbara.

But the other by-election in Kitchener-Waterloo turned into a close three-way race for the seat held for 22 years by Progressive Conservative Elizabeth Witmer.

McGuinty engineered that by-election by appointing Witmer to a $188,000 a year job as chair of the Workplace Safety and Insurance Board.

But political scientist Barry Kay at Wilfrid Laurier University says the strategy turned into a "negative factor" with voters, and predicts the Liberals will not get their majority.

The New Democrats made it a close three-way race, and hope for an upset in a riding they've never held.

Progressive Conservative Leader Tim Hudak says Kitchener-Waterloo was more of an Elizabeth Witmer seat than a Tory stronghold, insisting a loss would not hurt his leadership of the party.

The opposition parties said the Liberals picked a fight with teachers and recalled the legislature for an emergency session to distract voters from the scandal at the Ornge air ambulance service and the $190 million cost of shutting down a generating station days before last fall's election to save Liberal seats in the Mississauga area.

"It was a very cynical ploy that people recognized for what it was, and I think voters of Kitchener-Waterloo were really disappointed that the government decided to go in that direction instead of addressing the real issues they have there," said NDP Leader Andrea Horwath.