High YYZ HKG starts around Dec 15 or a date to coincide with beginning of week or weekend. Dec 17 being a Saturday we can assume that you have employment obligations to fulfill. High season ends about one week after New Years and starts again a few days before Chinese New Year.
Your chosen travel dates of flying out on a Saturday and back on a Sunday is also working against you for last minute seat availability and cost.

As a Torontonian I suggest you go door knocking at all the Chinese travel agencies in Richmond Hill, Scarborough, Markham, North York and Mississauga and be ready with the payment when someone gives you a fair price. I am guessing that most of them are within $5 of each other. Keep an open mind for routing through US and PRC.