By visiting DFO Cairns you will notice the many empty shops and places. Once they are filled, they will offer a day shopping experience with lots of choice. Currently, you won't spend much time there and real upmarket shops are still missing (only Ralph Lauren so far). The best way to get there is by car or by bus from the city centre (10min, around $3 per person one way). Walking time is around 45min, but not recommended.
Don't expect too much or imagine outlets in the US or other bigger cities.