The Toronto-Los Angeles route was flown with the 747, 747 Combi, L1011 and 767 at various times over the years. Larger airliners could be used since there was less competition on the route, there was less frequency on the route, and there was less choice - ie, there was far less transborder service back then. Thus, AC
used larger aircraft - also remember that back in the 70s and 80s, airlines in general utilized widebodies much more on short and medium range routes before airlines (especially those in North America) became far more focused on frequency and hubs and connections.
widebodies have also been used on routes into MIA
from both Montreal and Toronto (even DL
flew an L1011 on the Montreal-Miami route for a few years), and I think that larger aircraft were also used at certain times during the year on flights into Tampa. I also think that CP
(now part of AC
) flew DC10s on the Vancouver-LAX
route for a short period of time many years ago.