Its hilarious who you two farted about the definition. The Polynesians didn't suffer from overpopulation as defined by the West. The definition given, about a hundred replies ago, looks more to apply to Easter Island than either Tahiti, Hawaii or New Zealand. Whatever happened to wunderlust? In many instances it was entirely political events that caused people to migrate.
So if they had landed in Australia what would have happened? First off, theres no real proof that they never set foot on it. I think one problem is that the voyaging fleets were composed of a small number of canoes carrying a small number of inhabitants. I think its likely that at any place the Polynesians would have set foot on Australia they would have been outnumbered by Aborigines.