To sell to the Australian market exclusively, go to the Australian eBay site.
You can use your Canadian account.
You will have to list in Australian dollars.
You will have to use Flat Rate shipping.
Be very clear from where your item will be shipped.
If you are shipping from Canada, ONLY use Air Mail shipping. Surface takes months. (And there are more flights from Vancouver to China than there are to Australia, as anyone who has laid over at Vancouver airport can attest.)
Same with UK, go to the UK site, list in pounds, use Flat Rate Shipping.
Both sites allow you to ship only to the home country. Do this on your Seller and Buyer Preferences, not as a note in the listing.