As others have pointed out, it is very, very difficult to amend the Canadian Constitution in order to get rid of the monarchy. One might suspect that, back
circa 1980, some premiers believed that Pierre Trudeau was a republican and insisted on strong measures re: our form of government - a Constitutional Monarchy - in exchange for his Charter.
Just for the sake of argument, let's assume that Canada will remain a Constitution Monarchy. If we can't get rid of the monarchy, can we change the monarch?
It's been done several times: the "best" way, constitutionally, is the way Henry Tudor did it in 1485: he defeated Richard III in battle and seized he crown by right. Other ways include (1689) forcing the King to "abandon" his throne and usurping it. But there
might be another way - someone else, not long ago, mentioned the
Nickle Resolution which never passed the Senate and never resulted in an address to the monarch but, still, did its job ... the monarch, as he was required. to do,
Constitutionally (the one that's not written down anywhere), took note of the opinion of his Commons and, without being formally addressed, did as that Commons wished.
Suppose the Commons - the one in Ottawa -
resolved that
The Act of Settlement of 1701 is unacceptable to Canada due to the provisions (religious freedom) of our Charter. We might consider the case of Autumn Phillips (née Kelly) who was required (2007) to renounce her Roman Catholic faith so that her (former) husband Peter Phillips (son of Anne, the Princess Royal) could retain his (quite distant) position in the line of succession. Suppose the Commons
resolved that while Canada remains steadfastly loyal to Her Majesty the Queen, we do not accept the line of succession. In other words, we are loyal to the Queen but we do not agree that Charles should be king when she dies. IF this was both
resolved in the Commons and negotiated openly and honestly with the Royals, then
I suspect that the monarch and her "lawful heirs and successors" (Charles, William, George ..) would have little choice but to agree. Good manners, alone, suggest that no one would lay claim to a throne which did not welcome him or her.
Then what?
Well, there is a provision for monarchies, constitutional or not, to continue when the monarch is not able to reign - it's called a
regency. The last one that concerns us was 200+ years ago (1811 to `820) when King George III was barmy and his son, George, stood in for him as Prince Regent. IF Canada, for example, did not proclaim a new monarch on the sad death of Her Majesty then we would still be a Constitutional Monarchy, nothing in our Constitution would have changed, but we would be a monarchy without a monarch.
What to do?
Nothing much, actually ... we have a Governor General who has all her powers under the Letter Patent of 1947. It would be a stretch, but not a huge one, to say that she could, on the advice of her prime minister, appoint her own successor since there is no one else to do so. As long as we don't bugger about by changing how the GG is selected/appointed then we ought to remain on pretty solid Constitutional ground. The succession of GGs would be
Governor Generals Regent while, theoretically, we looked for a way to reinstate the British royal family ... but we would never get around to doing that and by, say, 2125, no one would actually remember when there was a real sovereign.
Is that idea Constitutionally sound and legal?
I don't know, but it's got a damned sight better chance of "working" than amending the Constitution ro make us republic does.I