Australia didn't have a choice.
The problem is, Do Canada have a choice as well?
If you look at the troop deployment in Canada, they very much depend on US intervention. Why I say this? Let's compare the Canada and Australia
Canada
land size : 9984670 sq km
Armed Force strength : 68250 Active, 47081 reserve, total 115349
Air Defence inventory : 103 Fighters (CF-188)
Naval Strength : 12 Frigate, 3 Destoryer, assorted loitering combat ship
Army Strength : 45,000 personnel 3 Infantry Regiment, 2 Armored Regiment, 1 Cavalry regiment
Australia
Land size : 7692024 sq km
Armed Force Strength : 57994 active, 44238 reserve, in total 102232 personnel
Air Defence Inventory : 95 (71 F-18C, 24 F-18E/F)
Naval Strength : 12 Frigate, 12 Patrol boat
Army Strength : ~ 60,000 personnel (2 Division, 12 Combine Brigade)
For a land mass of equal or larger size, the actual value of defence force is virtually the same. While the Australia are defending in principle on Delaying action so the US can mobilise their Asian Asset to get into the play, the same has been done to the Canada where instead of Asian Asset, you are talking about the US mainland asset to save their hidey.
Problem with such defending tactics require both Canada and Australia heavily rely on US equipment (So they can salvage and reuse when combined with US forces. Thus there are no other way but for Canada to depend on US import too.
US relation is very important to Canada, where there are literally no other choice but F-35 (Lighting cost almost the same as F-35, Gripen depend on US parts which US will simply reject for them in favor of other US planes, Rafale are crap for non-NATO standard weapon.)
Either F-18 E/F, F15 later version, it's literally F-18E/F vs F-35 in this case because F-15 cost 100-110 mil a pop, and F-35 already beat F-18E/F once, so that why I said, the US will offer some F-18 for stop gap, but ultimately the F-35 will win out.