I'm a United Premier Silver and booked a flight on AC next month to Japan. With United, i have access to Economy Plus (preferred), but only at time of check-in (T-24). I called AC and I inferred from what she said that I may be able to do the same on AC. I have to check in with United, as my first flight is on UA, but the ticket is AC. So I would have to call AC after checking in to try to get a preferred seat.

Can anyone help me to know 1) whether I'm understanding this correctly, and 2), if so, what are my chances of actually getting a seat, given the limited number of preferred seats?