You'd be crazy to buy anything international not purely on AC metal from ac.com if you ask me (especially business class), but the specific reason here is because the AC codeshare flights on SQ metal don't have D & Z class, only J & C. So YYC-YVR-HKG on AC and the AC6302 which is really SQ865. AC6302 looks like this in an request:
AC6302 J4 C4 Y4 B4 M4 H4 Q4 V4 W4 (notice the lack of D & Z)
You have to book the SQ flight numbers to get the SQ business service. So yes, speak to your TA or another human being.
Mendy7511 why don't you tell your TA about the fares you find direct from the airline, which are simply published fares after all? SQ is a sticky airline to deal with out of Canada and it could be something so simple like a mis-matched inventory bucket.
or better interline with KE, CX.