I know the colonists drove out the natives, but why didn't they have a Merican' style revolution? Were most of the colonists loyalists too? And why does Queen Elizabeth II still be the queen of the commonwealth?
Elizabeth II is legally and separately Queen of Canada; she is not Queen of the United Kingdom over Canada. Any question of this was completely resolved with the patriation of the constitution in 1982: https://www.royal.uk/canada
Moreover, the Queen is not Queen of the Commonwealth, but rather queen of sixteen realms within the Commonwealth. Her headship of the Commonwealth is not automatic nor hereditary.