Mississauga Mayor Hazel McCallion stood side by side with Wynne at an arts centre in the city as she gave the Liberal leader her nod of approval.
"As a leader, I'm endorsing her," said the 93-year-old McCallion, who is not running again this fall after more than 35 years in the mayor's chair.
Wynne took the opportunity to talk up what she calls her strong track record of working hand-in-glove with municipalities on issues such as infrastructure and transit.
"I believe that it is critical to the well-being of this province that the provincial government work with municipalities," said Wynne, painting the NDP and Tories as coming up short when it comes to dealing with local governments.
"We are the government, we are the party, I am the leader who has committed to continuing that relationship."
McCallion said the worst outcome of the June 12 election would be another minority government, which she said would leave municipalities "hanging" on legislation impacting them.
She also took shots at the Progressive Conservatives, saying their pledge to cut 100,000 public sector jobs would hurt municipal services and residents' "quality of life."
McCallion said Tory Leader Tim Hudak's plan has left major questions unanswered.
"If you're going to lay off staff, how is that service going to be provided? Just to say 100,000 jobs, with no backup material to prove it ... I don't understand it," she said.
McCallion urged voters to look at the issues and vote accordingly, and downplayed the ongoing scandal over the pricey Liberal decision to cancel two gas plants — one located in Mississauga — calling it "water under the bridge."
Speaking in Toronto, Hudak shot back, saying the election will be decided by voters and not city leaders.
"The ballot choice isn’t going to be what mayor is voting what way, it's going to be what leader actually has a plan to get people back to work in our province and make government work for you and people who are actually paying the bills, not the special interests," he said.
Wynne visited a Guelph school later Wednesday, where she read a book to an attentive full-day kindergarten class before telling reporters that Hudak's campaign ideas are "dangerous" and his platform would "undermine the institutions that define us as a province."
- With files from Maria Babbage
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