TORONTO -- All eyes will be focused on two Ontario ridings Thursday, where the results of the byelections could determine whether the province is headed for a spring election.

The votes in Niagara Falls and Thornhill, north of Toronto, which come on the one-year anniversary of Kathleen Wynne as premier, won't change the status of her minority Liberal government.

But they could prompt one or both opposition parties to pull the trigger on Wynne's government when time comes to pass the budget, expected next month.

The New Democrats didn't hold either seat so have nothing to lose and everything to gain, especially in Niagara Falls, a former Liberal riding where the NDP is in a tight two-way race with the Progressive Conservatives.

Political observers predict that an NDP win in Niagara Falls will prompt hawks in the party to pressure their leader Andrea Horwath to stop propping up the Liberal government.

"Even if they don't win the seats, as long as their candidates do better than they did in the last election, they can at least say we're going in the right direction," said Henry Jacek, professor of political science at McMaster University in Hamilton. "If they take Niagara Falls, they'll say" 'We're the real Opposition.'"

Horwath will also face pressure for an election if either her party or the Liberals take Thornhill from the Conservatives, one of the few suburban "905 ridings" around Toronto that the Tories hold.

PC Leader Tim Hudak wants an election as soon as possible and will push even harder if the Tories hold Thornhill and take Niagara Falls, which had been Liberal for a decade.

Hudak is the party leader with the "most on the line," said Jacek.

"If he can take away a seat from the Liberals, I think that would help him out quite a bit," said Jacek. "He's got to win at least one. If he loses both, then people are really going to believe that he's just not going to win the next election."

The Tories have a weak byelection record under Hudak, losing Kitchener-Waterloo to the NDP in 2011, although they finally won a seat in Toronto in a byelection last summer. The NDP have done much better in byelections, taking Windsor and London seats from the Liberals.

When word came last week that there would be a 2014 thoroughbred racing season at Fort Erie Race Track, one of the largest employers in the Niagara Falls riding, Hudak attacked both the Liberals and the NDP.

"(Former premier) Dalton McGuinty played these games and Kathleen Wynne does the same, when there's a byelection they hand over more money to advance Liberal interests," said Hudak.

"It was the weak and indecisive leadership of the NDP that allowed the slots to be taken out of the Fort Erie Race Track, and half those job losses are on Andrea Horwath's back."

A Liberal victory in Thornhill wouldn't be enough for Wynne to call a spring election, said Jacek, but if they also hold Niagara Falls it could change her thinking.

Jacek predicted the Liberals will try to get their budget passed this spring and hang on until the end of summer before going to the polls in a general election.

"There are a lot of people who don't think a May or June election is a good idea," he said.

"Now if she wins two victories she might be really tempted to say that shows in an election campaign we could roll the dice and win, but she might be tempted to go."

Jacek said the Liberals are leading most public opinion polls, but could "stumble" during a general election if voters don't like their plans for a toll or tax to pay for public transit expansion or to mandate payroll deductions for an Ontario Pension Plan.

At the same time, he said, Hudak faces unrest within the Conservative party over his controversial plans to make union membership and dues optional.

"Morale is already low inside the Conservative party for various reasons," said Jacek.

The New Democrats forced the Liberals to make several changes in the past two budgets, including a new tax on high incomes and a promised cut in auto insurance premiums.

They would be smart to try for more in the 2014 budget, Jacek said.

"It's important for the NDP to show they can get things done, particularly on economic issues, and (that) will really help the NDP's image."