Actually, On my recent flight to MEL, AC did through-check my bag all the way. I had to pick it up in SYD to clear customs, but merely dropped it off again at the domestic transfer desk without the need to re-tag it. Same thing on the return flight: while you do have to physically claim the bag off the carousel for customs purposes in YVR, the bag was tagged in MEL all the way to my final Canadian destination.

I flew AC 033/034 connecting with Jazz on this end and with QF down under. All very painless.