"This is a chance for some real answers from Dalton McGuinty," New Democrat Jonah Schein told reporters as he listed a series of questions the party plans to ask.
"Why did the premier's office destroy emails? What were the Liberals trying to cover up? When did Kathleen Wynne ask Dalton McGuinty about missing emails? Will the Liberals take responsibility for destroying key information about the gas plants, or will they continue blaming staff?"
McGuinty testified last month that he made the decisions to cancel gas plants in Oakville and Mississauga, which will cost at least $585 million, far above the $230 million he and the Liberals had originally claimed.
However, after his testimony, privacy commissioner Ann Cavoukian reported that top Liberals in McGuinty's office had deleted emails on the gas plants — despite legal obligations to retain their records — and even tried as late as January to permanently wipe email accounts from government databases.
The Ontario Provincial Police launched a criminal investigation earlier this month after complaints by the Progressive Conservatives about the destruction of emails by senior Liberal staff.
"I believe this is an orchestrated coverup from square one to try to cover the footprints on the gas plants scandal," said PC Leader Tim Hudak.
McGuinty should take advantage of his second chance Tuesday to set the record straight, and be more forthcoming and open this time, added Hudak.
"I hope that he'll use this second opportunity to take a different course than the first. I hope he'll be honest with taxpayers and tell us what really happened," he said.
"I just find it hard to believe, and I think most people do too, that senior people in the premier's office destroyed government documents without anybody knowing."
The NDP said Cavoukian's report raised some serious issues about attempts by the Liberals to destroy government documents that had already been requested by the justice committee, and they suspect McGuinty knew what was going on all along.
"The privacy commissioner's report was really clear and cast a tremendous amount of doubt about the honesty of the (former) premier and his transparency," said Schein.
"It's clear to us that the premier's office, and the government, has broken the law when it comes to privacy and making records available."
The Tories also believe McGuinty knew about the mass email deletions.
"I think premier McGuinty knew and I think Premier Wynne knew about the destruction of email documents. I have no doubt about that," said Hudak.
"It's not something that happens by accident. That happens as part of an organized campaign to hide the footprints."
Cavoukian will also appear at the gas plant hearings Tuesday, just before McGuinty's appearance, to talk about the conclusions of her investigation into the mass deletion of government email accounts by the Liberals.
"It is difficult to accept that the routine deletion of emails was not in fact an attempt by staff ... to avoid transparency and accountability," Cavoukian wrote in her June 5 report called "Deleting Accountability: Records Management Practices of Political Staff."
McGuinty denied he had a hand in the deletion of emails, but he resigned his seat in the legislature shortly after the privacy commissioner's report was released and has not publicly taken any questions on her conclusions. He will testify Tuesday as a private citizen, unlike in May when he was still the MPP for Ottawa-South.