Having flown on the 767 from YOW to YYZ, I love it - and it's swept me up out of LGA too. (A most welcome sight after a 4 hour delay). My fondest memories however on the 767 remain the YHZ to LHR flights (except when they went via St Johns) with Halifax based crew. Even the YOW to YYZ afternoon flight is done well by senior crew on a LHR / FRA - YOW - YYZ sector. (must be tiring for them too!)
I wonder whether an A330 fits this route better than a 787-8 though clearly not on cost. Down-gauging to a max would be such a retrograde move. Family in Halifax HATE the max to Heathrow. Having flown Toronto to SFO on a max, I now avoid it and would take an A320/1 or a wide body just to avoid the max.
The wider issue, and it will emerge again with the withdrawal of the E190s is whether the replacement within the fleet is a like for like replacement. The A220 is larger and may not fit the profile of the YYZ to YOW route. Mind you, neither is the A319 which is making more of an appearance on the route as a emergency replacement. Where we are used to a certain aircraft and size on certain routes, this modernisation and consolidation of aircraft types will change both how AC and PAX both think