Originally Posted by rankourabu

Assuming the flight is available via Aeroplan - the AMEX points will transfer immediately, and you can use them.

However, the transfer is irreversable, so you better make sure your redemption is available. Perhaps a good idea is to call in (and pay the $30 fee), and after the phone agent grabs the seats, hit transfer on the AMEX. They will be there within a minute.