I know people search for this kind of info so I wanted to post my opinions as I just got off my first AC 787-8 flight.

Row 31 BC and HJ have unlimited leg room but people congregate in front of those seats to use the bathroom and stretch/stand. I find that annoying so I chose row 18 seat C. While Row 18 has the bulkhead, it stops short of Seat C and Seat H and you can stretch your legs out fully. If you are real tall you may need to move your feet back when they push the beverage/food carts through but it wasn't an issue for me at 6'4". I also felt there was a good amount of leg room even for the bulkhead seats in Row 18 AB/JK. Normally I hate bulkhead seats because while the knee room is better, you can't stretch your legs out. If i tried to stretch against the bulkhead I made it about 90% of the way which is good enough, if you aren't very tall these seats would be fine. The middle section in Row 18 has slightly less legroom and on both of my flights had families with infants seated there. I prefer seat C for row 18 as you can easily use the lavatory a few rows up in Premium Y. On the HJK side, a curtain is closed prior to the lav during flight and it seems you aren't supposed to use that one.