The problem with a Cars attraction at Animal Kingdom (well, one of them...), is that there are no animals in the world of Cars.
As for what architecture to sure for an Australia pavilion beyond trying to re-create Sydney Harbour, as an Australian I am also drawing a blank! That said, the UK pavilion doesn't lean particularly heavily on architectural landmarks and could provide a model for a pavilion that leant more on either natural landscapes or some kind of non-specific city or townscape. Or just a collection of the "big things" we like to build as roadside attractions, e.g. a pineapple, koala, banana, etc...