Let's think about this. Australia and Canada (yes, Canada) start poking around near islands claimed by China and are completely shocked to find Chinese jets arrive to chase them off.
How would Canada and Australia react if Chinese surveillance aircraft got a little too close to their most distant claimed offshore islands? When answering, remember that the very thought of Chinese military ships being allowed to dock and take on supplies in the Solomon Islands (an INDEPENDENT country a few thousand km away from Australia) has Australia completely freaked out over how close those Chinese ships will be to their coastline.
Multiple countries have disputes over islands in the SCS. Multiple countries are building up some areas into artificial islands. Multiple countries are setting up radar stations and air defenses. Personally, I think countries that are not parties to the disputes sending in military ships and aircraft into disputed waters so they can bound their chests about the missions being legal and somehow important to Australian (and Canadian!

) security interests put the entire region at increased risk of an incident. Of course, that's always a great excuse for those outsiders to waste more and more taxpayer and gov't bond (borrowed) money on military hardware.
Remember, if it's OK for the US, Australia, and Canada to stick their beaks in, then they should be happy roll out the welcome mat for ships and planes from Iceland, Russia, Saudi Arabia, North Korea, Nigeria, Iraq, Colombia, Morocco, Venezuela, Iran, Somalia, Pakistan, Brazil, and more to join the party in the SCS and along the edges of claimed US, Canadian and Australian waters.