I lived in Canberra ACT for a brief 3 months and got to do a bunch of class 3-5 stuff in the area which was super fun. Hiking to the put-in of the Goodradigbee with a gang of kangaroos lounging about was one of my favorite experiences.
For general oz boating info, check out: https://www.adventurepro.com.au/padd.../#.VGDfwckhA8I
If you're going to be down near Canberra, here's the main internet forum: KayakCanberra.com
I never got to paddle up north, but I did check out the Tully, looked pretty sweet, and if you're up near Caines that's be a go-to for you. There a fb group for paddlers from around there: https://www.facebook.com/groups/5956228889/
The only drawback I found was that it was very hard to rent/demo a boat or any gear. Everything is about 50% more expensive in Oz so people were pretty reluctant to loan out stuff to a rando american chick. Also, I spent a week trying to go paddling in NZ, and ended up just soloing a lot of class 2. NZ in particular gets a lot of kayak tourists from the states who talk big but then eat shit, so people were kind of wary of boating with tourists. That may also have been because I was there in August (i.e. winter) so there weren't a ton of boaters around, everyone was skiing, but I really had a hard time rallying people when I visited NZ. BUT still one of the best trips ever, and you should be there at a more boater-friendly time of year. Have fun!