4engines,
I've flown both short and longhaul and enjoy both.Some friends of mine swear by one or hate the other,some like a bit of both.
What I'm saying is that only you will know once you've tried it.
The good thing at AC is that there is plenty of both and you can change aircraft type if you want to.
The thing is when you get hired you may get the choice between EMBRAER FO or 777 Relief that's about it.You'll then have to wait for your seniority to allow you to move to something else....every 6 months we have an equipment bid where you can bid off your type if your seniority permits.