Not sure about Brissy or the gold coast area, but any estuary would be a good place to start for species like Flathead and such. Good old clousers cast along drop offs and around weed beds. Can be fished from the bank, wading or out of a boat. Do it up here in the Pummistone Passage at Caloundra myself. Can't see why it would be any different further south. As for canals, BREAM around pontoons and maybe a chance of tangling with a Jack o two. Just make sure your a very acturate caster, as the fish hang tight to the pontoons and some residents aren't keen on people hitting their boats. I know I wouldn't be.
Just get out there and give it a go. Break some new ground. If it looks fishy, get the wand out and chuck some fluff.
Cheers
Billyboy