Just a few comments from my own experiences:

Winter / X'mas promo for HKG usually start coming out in July. High Price usually starts on Dec 1st at first. But towards end of Oct or early Nov, the dates usually push to around Dec 10th. For the core X'mas weeks, the AC "x days countdown to X'mas" promo usually cover 1 or 2 Asia / HKG promo in it. But only if you can really afford to book your ticket so late. If you do not need to travel AC, you can try CO/UA around May and June. As sometimes they have fare as low as $1200 for the core X'mas weeks

Due to the price of the tickets, for the last couple years, I had been using AEROPLAN and book reward ticket. This is when I can usually get more than $0.01 / mile return, especially when I do a stopover somewhere too on the same ticket. But it is hard to get the YYZ-HKG direct, usually only YYZ-(PVG or PEG or YVR)-HKG route. If you really only want YYZ-HKG direct, you can try picking an AEROPLAN ticket that start with an AC flight. Then on the date of departure, you can do a same day change fee of $100 for YYZ-HKG direct. But it is a very very very risky, as YYZ-HKG is a flight that AC do not have problem filling it during the X'mas time.

For travel agent, you can try "The First Travel Inc." where they usually run some promo for YYZ-HKG with either a "so-call" free stop within Asia, Free Octopus Card with $50 (I think), and 5 nights of hotels. Price usually goes around $1600 with all tax. But I do notice they start using CX over AC lately. If you do want AC, they ask for another $100 to $200 more.

Hope some of my info helps you.

Regards.

alc