"Political parties in the context of the campaign present commitments, then should they earn the privilege of forming the government, the responsibility is to honour those commitments," McGuinty told reporters after touring a factory in Guelph.
"That’s how democracy works," he said.
The premier took responsibility for the decision to scrap the Mississauga plant just days before last fall's election, but said taxpayers should not expect the Liberal party to help pay the bill.
"I made that decision at that time in my capacity as leader of our party," said McGuinty.
"When we earned the great honour of serving Ontarians as their government, I then made the decision as head of the government, as premier, to honour the commitment that we made in the context of the campaign. That’s what happened," he said.
McGuinty justified his decision to halt construction of a power plant his own government had approved by noting more condominiums were built in the area adding many more people to the neighbourhood.
"We listened to Ontarians who made a very compelling case that events had overtaken the original decision made some six years ago, some significant changes were there to be seen by all in the community," he said.
However, the opposition parties say McGuinty's last-minute decision was motivated by his desire to save Liberal seats in the Mississauga area, where opposition to the gas-fired plant was wide spread.
"I think that the Liberal government should be held accountable for this decision," said New Democrat Jagmeet Singh.
"It was clearly a seat-saving decision made on the eve of an election, and that’s why we’re calling for the auditor general to come in and give us a real figure of what the cost was."
Energy Minister Chris Bentley first said the cost of relocating the Mississauga power plant was $180 million, but the government later admitted there was another $10 million given to the developer of the project to halt construction.
There was "some genuine confusion" on the minister's part, said McGuinty, not an attempt to hide the true cost of the decision to halt the project and have the power plant built in the Sarnia area instead.
Bentley admitted Tuesday he should have disclosed the $190 million last week, even though some of the extra $10 million applies to another project by the same developer of the Mississauga gas plant.
"I think in light of the confusion it would have been much better to speak to all of the issues at the time," Bentley told reporters.
However, the New Democrats weren't convinced that the "confusion" wasn't a deliberate attempt by the Liberal government to downplay the total cost of cancelling the project.
"I tend to believe there seems to be some sort of lack of forthright honesty on the part of the (energy) minister," said Singh.
"When one minister comes out under question and comes up with an answer of $180 million (and) the next day the answer is $190 million, only after the media exposes the additional cost, I think that there’s certainly something here amiss that doesn’t sit well with me or with Ontarians."
There's still no word on the cost of the government's decision to scrap another planned gas-fired generating station in Oakville, which the Liberals cancelled after local opponents brought in activist Erin Brockovich to speak against it.