I'm not an expert about AAdvantage, but my understanding is as follows (for L class):
- BA flights will earn 25% of miles flown
- QF flights will earn 50%
- AA, LA/LP will earn 100%
- CX, JL will earn nothing.

You will get miles from London to Montreal. Only BA flights to/from the US are excluded (UK-Canada is OK).

If you post to QF instead of AA you will get 100% on QF and LA, 50% on CX, JL and AA, 25% on BA. Looking at your routing, it looks like you will end up with more points in this case. Anyway QF points are worth less than AA points in terms of "purchasing power".

I'm sure somebody will come up with exact calculations here on FT