The Progressive Conservatives accused Wynne of abandoning her principles when she failed to oppose her predecessor's move to cancel the plants, and the New Democrats said Ontarians were tired of what they called the Liberal record of scandals and "corruption."
The two gas-fired power plants were nixed under former premier Dalton McGuinty, a decision estimated to have cost taxpayers up to $1.1 billion in what opposition parties have said was a move to save Liberal seats.
Tory Leader Tim Hudak said Wynne betrayed her beliefs by being part of the cabinet that cancelled the projects.
"She faced a pivotal choice when Dalton McGuinty put in front of her a document to put a billion dollars into that hole behind me," Hudak said Saturday, as he stood in front of a construction pit in Mississauga, Ont., where one of the plants was supposed to go.
"She should have said no. She said yes. And that tells me now she's more about helping herself and helping the Liberals than helping you."
The Liberals scrapped the Mississauga plant during the 2011 election campaign and another in neighbouring Oakville in October 2010.
The provincial auditor has said much of the cost was due to various cancellation and compensation fees.
Hudak supported scrapping the plants at the time but told reporters on Saturday that if he had been in government the Mississauga location would have never been short-listed as a potential site in the first place.
The gas plants scandal — which has dogged Wynne throughout the election campaign — was pushed into the spotlight this week with a new development in an Ontario Provincial Police investigation into the deletion of emails and documents related to the projects.
OPP served the legislative assembly with a court order demanding logs showing who had entered the legislature.
Wynne has said the logs showing who was signed into the legislature between Jan. 2010 and March 2014 were not in her government's possession and she had no authority to direct the legislative assembly, which was co-operating with police.
But New Democrat Leader Andrea Horwath urged both Wynne and Hudak on Saturday to make it clear that they wanted the newly-sought documents to be turned over to police and to be released to the public.
In an open letter to her political opponents, Horwath said Ontarians "deserve the facts" before they go to the polls on June 12.
Horwath, who has described next week's election as a "referendum on corruption," said voters have tired of the Liberal government's disregard for taxpayer dollars.
"This is not a choice between bad ethics and bad math," Horwath said, taking a swing at job projection figures that have been questioned in the Tory platform.
"That ballot box decision that people will make will be to vote against corruption and to vote for a plan that makes sense."
Wynne, who has been adamant the police probe has not affected her office, cabinet or caucus, went on the offensive on Saturday, saying her rivals were merely trying to distract Ontarians from criticism of their own plans for the province.
"As Tim Hudak becomes desperate, he and his people say things that they know are not true," Wynne said in Waterdown, Ont.
"They want to stir up controversy and they want to make sure that we don't focus on what he's going to do."
Meanwhile the New Democrats, Wynne charged, had no coherent plan of their own.
"(Horwath) doesn't want to talk about what she believes she can do, because she hasn't made it clear what she stands for," Wynne said.
"People who don't have a plan, or who have a plan that is either flawed or they're afraid to talk about, all they can do then is resort to controversy or slinging mud."
Wynne said her party is the only one promising to "build the province up" while being transparent with Ontarians
"I have answered many, many questions about the mistakes that were made surrounding the relocation of the gas plants, I've taken responsibility," she said.
"The reality is that right now Tim Hudak and Andrea Horwath want to talk about anything but what they're proposing for the people of Ontario."
— with files from Colin Perkel, Will Campbell and Adam Miller.