A coach with a Flixbus (a major overseas operator) logo is operating in Canberra (seen this morning). Putting Flixbus into Google search reveals that Flixbus Australia is a thing, but the website seems yet to be fully responsive. Canberra - Sydney, - Melbourne appear but don't yet seem bookable. So watch this space.
FlixBus is pretty big in Europe as they have pretty cheap fares and go through many countries, they also operate FlixTrain in Germany too. On my recent trip and past trips to Europe I've seen multiple coaches operated by the company. They also operate in the UK too as I've seen them there too.
(https://live.staticflickr.com/65535/52782693187_05b305eeac_z.jpg)
In Bratislava, Slovakia (my own photo)
(https://live.staticflickr.com/65535/52792997484_9801b1a443_z.jpg)
In Amsterdam, The Netherlands (my own photo)
Deanes Coaches, not the former CDC Canberra/QCity mob AFAIK, are to operate the services out of Canberra.
Only $10 Canberra to Sydney & $0 to connect to the coach to Melbourne.
Looks like services start from 20 November.
I'm probably gonna at least try them to Sydney when I take a flight, I genuinely love the fact that they've got 1 am and 3 am from Canberra departures, it means that I can finally explore Sydney from 5 am to 5 pm instead of spending four hours on a train one way