All other things aside, Air Transat has the tightest seating to and from Canada. The A330 cheap seats have a 31 inch pitch and a 16.5 inch width. So being short and narrow is essential. The same airline goes to Toronto from LGW and it would be less painful to have a shorter flight and less doubling. The rest of it could be done as proposed. Of course, there are no FF miles on AT os there is no benefit to the longer route.