I got comp on UA to PremExec when I was a SE on AC.
You have to send some info to the program Go For The Gold. If I remember correctly, you send your last statement from AC and a photocopy of your SE card. It takes a couple of days to be comp.
The only thing is that if you have to fly on AC within Canada of to get to the US, you cannot upgrade anymore. But with cheap fare, I could never get upgraded anyway. Since I join UA and got comp, I flew only once in Economy on my last 200 flights. And I did manage to get to First on international flights twice.
Thanks UA and bye bye AC.