Australia has a slowish rail network because it is sparsely populated. It is an extreme version of America, the distances between population centers are quite large and there's not much in-between. There's also not much reason for anyone from Sydney to visit Canberra, and if you do, you certainly need a car to get around.
Sydney to Canberra centre for government adjacent business you probably don't need a car. The train is near parliament and probably near your office and hotel. Maybe a taxi to get to the city centre which is 5 min away.