I have never flown Air Canada. On most trips for the past 30 years I was able to check the bag through if the connection was less than 24 hours. On United in Jan. 2017 I was not able to check my bag through from MIA to Manila because I had a 14 hour connection in Honolulu. In August I have a flight from EZE (Buenos Aires) to Toronto, then connecting to Chicago after a 2 hour connection, then Miami. United now has a 12 hour rule. I am able to cut out the Chicago stop and fly directly to Miami. But this brings the connection in Toronto to 13 hours. If I need to reclaim bags in Toronto and take to the hotel I will not change from a 3 segment to a 2 segment trip. At 65 with a bad knee, and a retired attorney who has done discrimination work, thinking disability discrimination.
After 12 hours of travel the last thing you want to do is lug 2 large bags to a hotel.