With AC, you will get a pair of SSWUs which can be used on any fare, and a pair of SWUs which can be used on transAt and other international routes -- but not NAmerican -- from H-fares. These fares are only a couple of hundred $s more than the Q-fare you could buy on AC to fly from the UK to LAX via YYZ, YUL or YVR. So if you actually flew to NAmerica on AC, you can likely upgrade, albeit confirmation would not be until 4-days prior to flight.