AC is one of the three airlines left in Terminal B, along with AA
Originally, they were in Terminal B because that is where the old International Arrivals Hall was. That way, if the flights did not preclear for some reason, they could clear customs & immigration in Terminal B.
Since that time, the new IAB
opened and BDL
is trying to move everyone over to Terminal A. I'd imagine once the renovation finishes, they will move over to Terminal A and they might share gates with either UA
or US. If they ever fail to preclear, however, they will have to drop the passengers off way over the other side of the airport at the IAB
and then tow/taxi the plane back over to Terminal A for departure.