The issue remains. Canada is dependent upon the will of other countries when it comes to choosing its own Head of State.
That's not quite correct.
Canada made an independent and sovereign decision when it passed the
Succession to the Throne Act, 2013. That Act was considered and passed by both Houses of Parliament—the
Senate of Canada (which held comprehensive discussions on the matter), and the elected
House of Commons—before it received the Royal Assent. The decision to alter the rules of succession, for our country, were an entirely Canadian decision.
There is a major difference between subordinate decision-making (as you've suggested it to be) and collaborative decision-making between the
United Kingdom of Great Britain and Northern Ireland, Canada, and fourteen other
Realms of the Commonwealth of Nations.