Thanks all for your help and advise, much appreciated. This is a great and useful site.

In the end the AC flights didn't look too bad. We didn't get on the first one but got what seemed to be the last couple of seats on the later flight (864?) 3 hours later.

I was greatly impressed by the AC people, at LHR, YUL and in flight. Totally professional, but friendly as well. Now reading about huge cutbacks of staff at AC, and feeling a bit sad.