could Australia be invaded?, page-14

Well, in case you missed it, here is the Governor Generals website http://www.gg.gov.au/governor-generals-role

It quite clearly states he is hired by the Queen, and can:

1. The power to appoint a Prime Minister if an election has resulted in a ‘hung parliament’;
2. The power to dismiss a Prime Minister where he or she has lost the confidence of the Parliament;
3. The power to dismiss a Prime Minister or Minister when he or she is acting unlawfully; and
4. The power to refuse to dissolve the House of Representatives despite a request from the Prime Minister.