I'll miss Jazz on the YOW-YTZ route, which I found extremely convenient. If I was down in Toronto for work and decided to return on the weekend when Jazz wasn't flying, I would take VIA instead (but never bother with the trek out to Pearson).
If the airport allowed it, I think that Jazz could profitably build up to a more frequent schedule on larger aircraft.
The biggest thing the route had against it, though, was lack of promotion by AC and the fact that the standard rail COS for government employees is VIA1.