If flying TATL - try the Aeroplan/esso extra/RBC rewards/BA shufflle (when RBC to BA has 50% bonus- current offer expires Jan 31,11) - works out to about 2% extra BA miles vs aeroplan (100,000 aeroplan abot 102,000 BAEC miles) . Only works if you belong to these programs obviously.

BA YYZ - LHR often has 6-8 reward seats in J. Taxes and surcharges right now are cheaper on BA.
Way, way easier to get seat on BA, often at a month or 2 notice.