I don't know the major difference but I know that the A340-500 have PTV in Y whereas the A340-300 doesn't.
I don't know the other major difference but enjoy the view when the aircraft is taking off!!! I guess you will get a better view of the surface on the A340's (not an insult) opposed to the B744 which I think is a good thing.
Oh but one thing, when you stop in YVR
, enjoy the executive class lounge of Air Canada. I don't know if its only the arrival lounge but I hear they have showers and they even clean your jacket or clothes while you are taking a shower.
Flown on: DC-10-30, B747-200B, B747-300, B747-300SR, B747-400, B747-400D, B767-300, B777-200, B777-200ER, B777-300