If the Japs had landed in Australia they would have had a very hard time.

Most likely they would have landed via Papau New Guinea as the straits between us and them would be easily controlled by Japanese air cover. However, at that time the roads in Northern Australia were usually not much more than dirt tracks and distances between towns in the north and the main cities in the south is pretty far. Most of the industry etc is in South eastern Australia so armament production would not have been affected for quite a while.

And yes, just about every Australian male knew how to fire a rifle. The Japanese would have been facing a very determined civilian population. They had a very hard time fighting the Australians in New Guinea, being beaten on more than one occassion by outnumbered Australian troops.

Imagine what they would have had to face on the Australian mainland. Aussies don't take kindly to people trying to take over and tell them what to do. Besides if worse did come to worse and they did manange to totally control Australia, I'm pretty sure a hell of a lot of Aussies would have gone to New Zealand to continue the fight there.

And I'm pretty sure the US would lend a hand. There were a lot of US troops in Australia, MacArthur had a HQ here, and the US Navy had warships and submarines operating out of Australian ports.

The war might have lasted longer in the Pacific, and yes maybe they would have bypassed Australia until they had dealt with Japan itself, but it's highly unlikely the Japanese would have had a very easy time.