Routing through SIN and NRT/PVG/PEK is not possible with any Australia/NZ destination except Perth - they are all over MPM.

For example, from SYD, pretty much all that works is SYD-ICN-YYZ-YOW or SYD-PEK-YYZ-YOW (it's just under MPM5). Routing through YVR is also over.

From MEL, I found that MEL-PVG-YVR-YOW is bookable. MEL-PVG-NRT-YVR/ORD-YOW also seems to work. The key is you must fly direct from MEL-PVG/PEK.