I live in Sydney and had worked in Canberra for about 9 months. Canberra does not have much tourist attractions but it is still worth going. Canberra does not have international airport so you have to go to Sydney and take a coach to Canberra, it only takes about 3 hours. Do not take the train, for it is more expenisive and takes 4 hours.
There are lots of day tour (or 2 days tour) from Sydney to Canberra.
I don't think there is any tourist to go to Canberra alone. I think you better of to take the tourist to go to Sydney first, then take a local tour to go to Canberra. Because there is not much to see in Canberra anyway. The most you need is 2 days, you can see everything in there. Actually there are more to see in Sydney, you should spend more time in Sydney then in Canberra.
Otherwise you can stay behind after you finsih the Sydney tour, then get a train ticket to go to Canberra.