I am thinking on my upcoming YYZ - BKK trip to do AONE3 and go west on AA, then CX to HKG and BKK then go home on QA or BA from BKK to LHR and then to YYZ. To try out a few carriers F class and so forth and frankly conencting in London might include a day there or two since I haven't been.

When booking flights are "A" seats generally available or is it akin to award seat travel with its limited "C" and "R" and "X' seats? I'd hate to want to try changing the route (or even trying to set the itinerary at the outset) which I understand is permitted after you start and then find it is impossible to find seats.

The YYZ-BKK route on CX in F (assuming they have F when I go which they don't) costs more than double AONE3 so obviously AONE3 is a good deal if it can get me there and back when I want to go.