We have twice booked cruise airfare once to SJU and the other to MIA. The cruise lines won't let you pick your seats and only let you know your flights 1-2 weeks before departure. Both of these trips were done during march break.

Our SJU flights were as follows

YYZ-ORD-SJU down
SJU-MIA-IAD-YYZ back.

Almost all of these flights we had to ask for seat swaps. I even called the airlines to book the seats and they said no. The one flight was pretty easy as we were both sitting next to the swappers spouse in the same row. Most times we let the GA try and move us and not ask for a swap. I think we only ended up apart 1 flight.

The other flight we got AC direct YYZ-MIA. The papers I got said I could checkin 24 hours ahead online and pick our seats. When I logged in I noticed we were assigned 1DF in both directions. I don't fly much so didn't know where these seats were and thought we were not sitting together. I later found out we had been given a full J ticket with all the benefits. Not bad for $420/person @ march break.