Thanks for all the help folks. I don't have any easy (cheap) way of getting to YYZ, so it does have to be YVR. I'll see what BA say, and get there in plenty of time in case i need an endorsement. At least both AC and BA seem to be in the same terminal. And if I really get stuck, maybe AC will let me go to FRA instead, and I'll make my way back to the UK from there.