I agree with the comments about the quality of AC's Executive First (i.e. business class) plus you will get to use AC's Arrivals Lounge in London which is also a treat after a transatlantic trip.

A vastly superior product to U.S. airlines business class.

And AC is supposed to be working on the food to bring it up to CP's standards -- we'll see! I'll get a report from my brother who just flew back last night on Executive First to London.