Flights are very frequent and only take about 25 minutes but by the time you get to the airport, through security etc it is just about as quick to drive. It is a great road too - literally three turns and four lane highway all the way from the centre of Sydney to the centre of Canberra. There are also hourly buses that lots of people take to get down to Sydney for cruises and back and take 3.5 hours (e.g. https://www.murrays.com.au/express-services/canberra-sydney-timetable/) and the train (which is less reliable but still nice). Let me know if you do decide to come to Canberra and I can provide more advice. 🙂