I flew Gatwick to Mirabel with Air Transat last year. You should be warned that although they do operate A310s on the route, they also use TriStars.
lthough ancient, it's a far better a/c in terms of leg room etc. Unfortunately, if you get a L1011. expect to tech stop in Gander for fuel. Arrived in YMX 3 hours late. Still better than a flight in one fo their Airbuses though...appallingly cramped!
On Sby