To be honest, I don't think there is an aircraft that is comparable to the 757 when you look at the routes it can operate....
Tricky one to solve really......
The obvious way is 767 or A330 for the canadian routes but that means increasing the capacity....
OR
A321 / B737 ......and sell the canadian flights to a 3rd party.....
I know which my money is on.....and it isn't on growth!