According to SeatGuru, Air Canada has three versions of the 777-300ER High Density (with 3-class seating) in their fleet. In mid-July 2016, we flew YVR-LHR and then LHR-YVR. Both directions we were in row 18 H,J,K. On the YVR-LHR leg we were on a version 3 aircraft. There was no bulkhead between economy and premium economy so we had great leg room and were able to stow small bags under the row in front of us (except for the aisle seat). On the LHR-YVR leg we were on a version 2 aircraft. This aircraft had a bulkhead between economy and premium economy and I did not feel like there was adequate leg room. For the person sitting on the aisle the bulkhead only extended half way in front of this seat, so you did have more leg room. However, you would occasionally get hit by a cart or passenger moving from the wider aisle in premium economy to the narrower aisle in economy. You also had to stow small bags in the overhead on version 2. On both versions, the seats are a little narrower due to the tray table and video screen being in the armrest. I am 6'3" and 220 lbs. I felt like the additional $69 (US) per seat I paid each way was reasonable for row 18 on the version 3 aircraft but not on the version 2 aircraft. Your best option on a version 2 aircraft is probably row 51 H,J,K.