I'll be going to Canberra and Sydney for vacation in two weeks and would like to know if there are any good hobby shops in either city. I'll have access to a car in Canberra, but not in Sydney. Any advice would be greatly appreciated!

Hi mate.
I don't know about Canberra

It's been several years since I've been but Hobbyco in Sydney used to be a major player and as far as I know still is. Just google Hobbyco Sydney. It's easily accessible in the city from the train.

Only other ones I know are in Melbourne.

Enjoy your trip