Would there be a market there? I can see Niagara, from a tourism perspective. Imagine being a 30 min (if that long) plane ride to a day at the falls? Maybe Kingston for the University crowd. Windsor? Not much there other than the border crossing to Det, might as well land in Det. London? Maybe, but again what kind of market is there. Sudbury maybe, but they are already serving Thunder Bay. What they should do is work out an arrangement with some bus company (greyhound?) to run routes from the Thunder Bay airport to the other Northern ontario towns.
Collingwood would work from a tourism perspective as well, and maybe Sarnia as well.