That's a sizeable tub (assuming the width is proportional to the height you quote) so the gracefully arching fronds of a small-to-medium sized tree fern would look really good. I'd check out a good nursery in your area and see what tree fern species seem to be suitable for your local climate. The most common types are Dicksonia antarctica - which might prefer it cooler than your area - and Cyathea cooperi, which will outgrow a tub after a few seasons. My personal recommendation would be Cyathea brownii, if you can locate one for sale - I think don't think that's impossible to track down in your state. The best nurseries might even have Cyathea robusta and Dicksonia youngiae too, which are proven Queensland varieties. As long as you can provide permanent moisture, a tree fern in a very large tub makes a wonderful fronding showplant.

Thanks for your suggestions step!

Just realised that I've implied Cyathea robusta is a Queensland native (when it's actually from Lord Howe Island, although it's sure to be available from some specialist Queensland suppliers).