I'm not 100% sure, but you can also consider breaking it into two flights, by taking the YYZ-YVR portion 1h earlier. Originating in YYZ you are spoiled for choice after all

Doing so is also beneficial to your mileage balance because a single flight number credits to your mileage program of choice as a single flight from origin to destination, albeit in this case it's just an extra 250.
http://www.gcmap.com/mapui?P=YYZ-YVR-SYD,+YYZ-SYD
In certain cases, US Air in particular, it can make a huge difference:
http://www.gcmap.com/mapui?P=TPA-CLT-IAH,+TPA-IAH