Ontario Liberal Leader Kathleen Wynne denied Monday that her party's recent TV campaign ad directed at NDP counterpart Andrea Horwath is an attack ad, saying the spot simply contrasts the policies of the two party leaders.

Wynne, speaking on CBC Radio's Metro Morning, was asked by host Matt Galloway why Wynne went with a negative ad so early in the campaign. Wynne has said she wants to avoid negative personal attacks against the other leaders.

In the 30-second ad voiced by Wynne, she describes key elements of the Liberal budget the NDP rejected two weeks ago, a move that triggered Wynne's call for the June 12 provincial election. The ad ends with the question "is Andrea Horwath for real?"

"It's a contrast ad," said Wynne. "We put forward a budget that made investments in the social fabric, in our infrastructure, that put in place support for retirement security. The NDP voted against all of those things and I think people need to ask 'well, why is that?'"

Galloway suggested the distinction Wynne draws between a "negative" or "attack" ad and a "contrast" ad is largely semantics. Wynne insisted she's simply trying to illustrate the difference between the policies of the two parties.

"It would be naive to suggest that as a leader running against other parties that I wouldn't put forward our position in contrast to the other parties," she said. "All the things the NDP voted against are things that we stand for. The NDP didn't engage with us and I think it's legitimate for us to ask that question, 'why?'"

'Mistakes were made' by McGuinty, Wynne says

Galloway also asked Wynne whether voters could trust her party in the wake of the ongoing controversy over the cancellation of two gas plants, a move that will cost taxpayers up to $1.1 billion.

The decision to cancel the gas plants was made by former Liberal premier Dalton McGuinty during the 2011 provincial election. Wynne succeeded McGuinty as Liberal leader and premier in January 2012.

"There's not a government in history that hasn't done things they could have done better," said Wynne. "The measure of a politician is how you respond to issues. How do you deal with mistakes that have been made and how do you move forward? And that's what I've been doing."

"[McGuinty] did what he believed was right. There were mistakes made. I've been clear that there were things that I didn't agree with."

"[The Ontario Liberal party has] been in office since 2003. There's been a lot of good that's been done over that period of time. I stand behind that and I'm proud of the work that we've done."

Police are investigating the deletion of emails and documents about the gas plants.

Wynne has also launched a $2-million libel suit against the Progressive Conservatives over their comments that she "oversaw and possibly ordered the criminal destruction of documents" related to the plants.

The Tories have denied any wrongdoing.

With files from The Canadian Press