splash&dash
you would think there's demand for a year round YYZ
The problem with Canada is it's principally a VFR destination, and the "R" (relatives) part of that acronym are dying off. This is why many airports that used to enjoy summer only services, the likes of LBA, EXT, STN have lost them, and BHX has lost hundreds of seats per week since the hey day of Wardair 747s and DC10s 3 x weekly.
If you're going to visit Canada for a holiday, the depths of winter aren't the ideal time - it's too perishing cold, and apart from for Christmas (and I can't see why a TS series over the festive season wouldn't work from BHX) you'd be hard pressed to find enough passengers to make a winter service pay.
I think we should be happy we've clung on to the once-weekly summer only YYZ operation. The extended runway however, could bring forward the possibility of weekly ITs to Calgary during the ski season - if of course the tour operators want to risk diluting demand for Manchester and Gatwick services to offer it.