I never book tickets with my middle name. United put my middle initial after my first name and stuck my salutation on it so the ticket read
Lastname/MissGJ83MI
Australia didn't care about that, they were more concerned with having the street address of where i was going to be staying.
When I go to Canada I book through my travel agent instead of United's call center so my tickets read Lastname/GJ83. Canada is more concerned with me traveling on business than whether I have a middle name or initial on my passport. I believe everyone in the US with a middle name gets it on the passport and now on drivers licenses too.