1) Never been on it, but I would say do this if at all possible
4) This would be a good second option, considering you'd still get the FCT and LH first for the bulk of the flying, and I don't recall ever hearing anything ranking LH F below UA F.
2) I've done the opposite direction (admittedly in Y) but it wasn't fantastic. Nothing special, but nothing bad. If the first two don't work, yes.


3) I'd go ahead and say no on this one. AC is still phasing in the new cabins on most of its LHR routes and the odds you'd be looking at an old 333 or non-XM'ed (aka old) 763 is just too big. I do quite like the J product on the 777 and can only assume it's similar on the XM'ed 763s, but it's still not quite a 1st experience and as someone who actually likes AC, I'd rather your experience with them be optimal. The flight to LAX would likely be on an XM'ed plane, and while the domestic J config is better than intra-europe J, it's nowhere near the standards of AC Intl J, let alone F. Not to mention that Calgary sucks.

And their airport isn't that special either.