I've recently come across these two photographs. They appear to be of the same ship and the upper photograph has "HMAS Canberra 1940" written on the reverse. The other photograph seems to be of the same ship.
Some other photographs in the set were taken in Sydney Harbour from the Manly Ferry, so I think it's likely that this was taken in Sydney Harbour too.
I'll check with my friend Mac Gregory who served in HMAS Canberra and see what he thinks.