At the risk of sounding cynical, AC charges that much because they can. I remember plenty of ~$1000 flights to HKG from YEG/YYC/YVR back before TPAC Tango. I somehow doubt $1200 for T+ to BKK from Canada in 2012.

Why not just fly someone else? I see YVR-BKK in Premium Y on both BR and CZ for $2000 and C on HU for less than $3000. If you're looking for absolute cheapest, there's plenty of airlines with decent fares to BKK in Y.