I don't know how you are routed for BRU and how much time you have, but you can always (to get the extra miles) buy a YYZ-LHR-BRU ticket, and a BRU-LHR-YYZ ticket back to back. You'll notice the BRU-YYZ ticket is significantly cheaper.

Generally not cool to do, but if you fly all the segments, then the airline won't care that much.