Based on my experience and what I've been told, the later flights are not anywhere close to full except on Friday when all the business people return home. Even when it's full it's people travelling on cheap NITE fares. CP/AC did have some late evening departures out YYZ prior to the winter schedules but loadings were just too low, on some days J class was totally empty on the A320s a day or two before departure. They cannot survive simply flying low yield Y clas people and upgraded SE paying cheap Y fares. They need the J paying passenger and most of them fly afternoon flights out of YYZ which is why they use the 767s/333 during the afternoon and 320 during the late mornings and early afternoon.