Canada is no longer part of the British Empire. Neither is the US, since the end of the War of Independence. That’s what independence means.
So Elizabeth was a British monarch on Canadian money, and Canadian monarch on Canadian money, uniquely.
Of course she is no longer put on newly made money.
Americans had 200 year dramatic and violent head start and everyone has figured that out by now. The details of Canada’s status are understandably less well known.