Originally Posted by
margarita girl
Don't know if this will work, but how about booking your ticket online YYZ-BKK-YYZ (or just putting it on hold), and then calling AC to change the date on the BKK-HKG or HKG-YYZ segment so you have your 10 day stopover. If they won't do it, you can just cancel the ticket assuming you do this within 24 hrs of booking it.
If you explain to AC that this is what you wanted to do, but could not do it online due to multi-city limitations, they might help you out.
I think the problem with the multi-city in this case is that the HKG-BKK segment is a codeshare operated by TG and it appears on ac.com only if booked in conjunction with a segment operated by AC either right before or after. As soon as you try to book this leg separately, it is no longer offered and the website tells you that there are no flight between the two cities on the specific date. This happens for any codeshare flight not operated by AC. Now, what I don't know is whether this is only an issue with the website, or some general rule used by AC. Last, if I remember well, the ticket rules for this trip allow for one stopover, so I think margarita girl's suggestion is well worth trying.