The standing committee on justice policy already grilled McGuinty's former chief of staff Chris Morley last week. McGuinty's testimony on Tuesday will be his first time commenting publicly on the controversy since privacy commissioner Ann Cavoukian slammed the wiping of the emails in her report, calling it a violation of the province's record-keeping act.
In questioning Morley last week, committee members alleged that the deletion of the emails related to the gas plants was an attempt to cover up the true cost of the cancellations.
The Liberals had initially put the price tag at far less than the current $585 million cost.
McGuinty was called to Queen's Park last month to testify about when he learned of the costs of the gas plants. This time, the focus will be on Cavoukian's damning report that senior Liberal staff deleted the gas-plant emails.
Cavoukian to testify first
Cavoukian will testify in the morning about her scathing report, which blasted the former premier's office for a "culture" of not putting anything about the gas plants in writing.
McGuinty will follow with his own testimony in the afternoon.
Progressive Conservative Leader Tim Hudak said he wants McGuinty to answer some compelling questions.
"I hope that he'll use this second opportunity to take a different course than the first," Hudak said. "I hope he'll be honest with taxpayers and tell us what really happened."
New Democrat MPP Jonah Schein has questions of his own.
"What were the Liberals trying to cover up?" he asked. "There's not a very good record of transparency when it comes to this government."
Tuesday will be the last day of gas-plant hearings for a month.