Premier Kathleen Wynne hasn't yet called a by-election in Whitby-Oshawa to fill a vacant seat in the Ontario legislature, but she's already running radio ads promoting the Liberal candidate.

The by-election must be called by February to replace former deputy Progressive Conservative leader Christine Elliott, who resigned her seat last summer.

In the 30-second radio spot, Wynne says one of the things she's most proud of is that Ontario no longer burns coal to generate electricity, and now has more wind and solar power on the grid.

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She also suggests the other parties could bring back coal-fired power generation, even though the Tories and New Democrats have no such plans.

All three parties have nominated their candidates: Niki Lundquist, a labour lawyer, is carrying the NDP banner, regional councillor Lorne Coe is the Conservatives' candidate while Elizabeth Roy, a former school trustee, is running for the Liberals.

Elliott, the widow of former finance minister Jim Flaherty, quit the legislature after losing the PC leadership race to Patrick Brown, and last month was appointed as Ontario's first patient advocate.