If you take
Air Canada to Sydney, you will pick up your bags at Sydney and go through Customs. Immigration might ask you the purpose of your visit but you should indicate it on your incoming passenger card which will be handed out to you on your flight. There will be beagle dogs sniffing your luggage as you await in the carousel area so do not bring any illegal drugs with you and declare ALL food; don't bring in any food that you might have bought in airports or received during the flights. There are strict quarantine measures in place. Even a tin of beans has to be declared. Any items made of wood ie jewelery or picture frames must be declared. You will be given a card to inform of you of what you must declare and what are prohibited items/materials.
So, once you go through Customs you will be asked to put your luggage on a conveyor belt to be scanned. If the Quarantine agents find something they are unsure of you will be asked to open your luggage. Make sure to have any and all prescriptions labeled appropriately with your name, the medication name and the doctor's name; leave them in the bottles originally dispensed.
Once you clear those 'hurdles' --- it's a breeze really -- then leave T1/T2 (international arrivals) and take the shuttle to the domestic terminal. If you aren't sure just ask. Last time I went through SYD there were individuals who were designated airport guides scattered around.
You should be issued with all boarding passes right through to Melbourne when in Canada, but if not go to a Qantas counter and receive your new domestic boarding pass. Go again through the screening area and then wait for your flight. The
flight from Syd to Mel is roughly 1.5 hrs.
Good luck with Air Canada; they have a propensity to missplace baggage! But they always find it. LOL. My husband went to visit me once and took the SYD to YVR to YYZ route and his (and hundreds of other's luggage) went waylaid somewhere; he showed up in TO without anything save for his carryon. As for carry-on bags, take a small one and keep all your meds and docs/passport/credit cards in it. Never pack anything of value in your checked baggage.
You might not bring more than 50-100$ aud until you arrive on Aus soil; the exchange rate at a Canadian bank will be dismal. Don't forget that the Aussie dollar is higher than the Canuck one at the moment, so it'll cost more Canadian to buy Australian money. I found that I got a better rate using my debit card or credit card from an Australian ATM. Better get informed as to how much your Cdn bank will charge per transaction.
Hope this helps. Good luck!