TORONTO - Ontario Premier Dalton McGuinty won't say if he will end the looming transit strike that threatens to slowdown Canada's largest city.

As the Toronto Transit Commission and its largest union continue to negotiate toward a 4 p.m. deadline on Sunday, McGuinty will only say he's optimistic a deal can be reached.

"I'll tell you why I remain optimistic. I believe there is a tremendous amount of goodwill at the table," McGuinty said following an event at Toronto's Royal Ontario Museum.

"I think there is a tremendous amount of mutual respect and a very profound understanding of each side's respective challenges. I also believe that there is a sincere desire to find a solution that doesn't compromise services for commuters."

After being widely lambasted Friday for saying he would consider declaring Toronto transit an essential service - which would prevent the union from striking - McGuinty stuck to a cautious script Sunday.

"I just remain so optimistic that the parties are going to find a solution," McGuinty said repeatedly, regardless of the question he was asked. "I'm trying to deliver this differently every time now. You ought to observe that."

Late last week, McGuinty said both sides have a "heavy responsibility" to ensure they reach an agreement. Failure, he said, is not an option.

But as the talks continued down to the wire, McGuinty refused to say how long the province would allow a strike to drag on if negotiations fail.

The head of the Toronto Transit Commission's biggest union doesn't seem to share McGuinty's optimism. Bob Kinnear is warning the system's 1.5 million riders to make alternate travel plans for the Monday commute.

Talks between the TTC and the union are at a standstill, he said, adding demands over wages and benefits haven't been met.