Supposing the big lemon (YYZ) is your final destination, it would probably make the most sense to book SYD > YYZ as a return ticket on QF using points. There are several benefits I see here. First the points cost should be lower since you are paying for one ticket instead of two (Qantas uses the mileage flown to calculate points required when you have connecting flights). Second it would make connections smoother. For instance, suppose your Qantas flight to YVR gets delayed and you arrive late and miss your connecting flight. Well since it is on a separate itinerary you are on your own (in theory) whereas if it was booked on one itinerary, QF would be forced to sort that out for you (since they were the carrier that caused the misconnect). Second, in terms of baggage, you would only have to worry about it once: at check-in when departing SYD and also in YYZ. You wouldn't have to worry about extra bag fees since IATA's most significant carrier (MSC) rule would apply and since Qantas is the first carrier crossing an IATA zone, their baggage rules apply. Third you could potentially have the advantage of One-Stop-Security (OSS), which some participating airlines flying to Canada support. What this means is when you land in Vancouver, yes you'll clear Canada immigration at one of the Kiosks but once you are done you are directed to the domestic departures hall. You won't need to go through security. You won't need to collect your bag. Makes connections super seamless.
Good to know!
I will point out that depending on your frequent flyer status elsewhere, you can get some of these things for free. For instance, I am a Delta Gold Medallion member and as such, once I enter my Delta number into the WestJet site, I can select any seat I want free of charge. Similarly I get 2 bags (up to 32 kg each) for free. Now obviously if you don't have Delta status this is a red herring, but at least before next year it was super simple to get via status match (essentially fly 12,500 miles on most SkyTeam airlines and you'd have yourself Delta Gold status).
-RooFlyer88