Option 1 is workable.

Option 2 only works if your arrival time in CAN on the way back from SYD is less than 24 hours before your flight leaving PVG (the 48 hour rule only applies to certain passport holders for both entering and exiting China in Shanghai; the default for anything else is 24 hours with two stops inside China). On the way out you could add a stopover in CAN though.

Option 3 is not workable. The airline will not let you board the flight (56 > 48).

What are you defining as a cheap option? Maybe worth also considering flying back through Hong Kong and getting new visas there? You might be able to offset the cost of the visas with a better price (for a 2 week trip in Jan I am seeing 7800RMB for PVG-SYD-MEL-HKG-PVG on Quantas).