You realize that we choose to do that, don't you? The British have no say in how we govern, nor what we do. We pay nothing to the British gov't, nor to the royal family.
When the Royals are invited visit, we pay for it, but so do all the other countries that they are invited to visit, including the US.
We stay in the Common Wealth by choice. The Common Wealth has many benefits for trade, travel, work visas and more.
The Governor General is there as a symbol and is a ceremonial function, nothing more. It's to pay homage to a history, and has been part of parliament since the start. The appointment is basically made by the PM as he says who he wishes to have appointed and the Queen rubber stamps it. It's part of tradition.
You should really learn more about your own country because to say we're not free and/or are slaves to the Monarchy or England is just asinine.