Ontario Progressive Conservative Leader Tim Hudak demanded that Premier Kathleen Wynne call an election over her Liberals' billion-dollar cancellation of two gas-fired power plants in the Toronto suburbs.

The man who ordered the cancellations, former premier Dalton McGuinty, defended his decision but conceded his government made a mistake in even trying to build the plants in the first place.

These twin developments Wednesday came a day after Auditor-General Bonnie Lysyk revealed the full cost of pulling the plug on one of the projects, in Oakville. Combined with the earlier total for ending the other plant, the government will end up shelling out up to $1.09-billion. She also found the gas-plant costs were much higher than they needed to be because Mr. McGuinty's staff meddled in cancellation talks.

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"Kathleen Wynne and the Liberals should step aside now and call an election," Mr. Hudak said at Queen's Park. "Let people cast judgment on this government. I mean, enough is enough."

Earlier this year, the PCs tabled a motion in the legislature to force a confidence vote on the gas plant matter. But under a quirk of Ontario's parliamentary procedure, that motion can only come for a vote if the Liberals agree to it. That rule is unique to Ontario; in other provincial legislatures and the federal Parliament, the opposition does not require the government's permission for a confidence vote.

The New Democrats refused to back Mr. Hudak's call for an election on those grounds. Since the opposition cannot force the confidence vote, Leader Andrea Horwath said, the matter is moot.

"Mr. Hudak can stand on his head and spit nickels, but he's not going to force an election in the province of Ontario," she said. "It is irresponsible to pretend that he can do that."

Mr. McGuinty, meanwhile, said he partly "regrets" the way the gas plant matter played out, but would not apologize for what happened.

"It was wrong to locate a gas plant the size of a hospital beside a hospital and a school and family homes," he told reporters in Elliot Lake, Ont., where he was testifying at an inquiry into a 2012 mall collapse. "I regret the fact that it has cost so much, I regret the fact that we hadn't acted sooner as a government. But it was right to relocate those plants."

Even though Mr. McGuinty scuttled the plants, Ms. Wynne has taken political responsibility for what happened.

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"There were mistakes made," she said in the legislature Wednesday. "I have apologized and I do apologize for those mistakes. But my responsibility now is to make sure that this never happens again, that we have the processes in place to make sure it never happens."

A legislative committee is also investigating the gas-plant cancellations and must decide whether to pursue a contempt of parliament charge against the government. Mr. Hudak would not say Wednesday when the committee will make its decision.

The next election is not scheduled until the fall of 2015, but the government must face a confidence vote at next spring's budget. Ms. Wynne can also call an election at any time.

The cancellation of two gas power plants in Ontario will cost roughly $1-billion, according to Auditor-General Bonnie Lysyk — much higher than what was estimated over a year ago. This chart shows different estimations over time, dating back to July, 2012. Read the full story on the cancellations.