Here’s my point of view: it would be extremely simple to change our system to give reduced powers of our Governor General to an unelected president named by our prime minister every five years.
But because the Canadian government rammed the constitution down the throat of the Quebec government, any constitutional change is now a political impossibility. And now Indigenous groups are demanding a seat at any constitutional discussion, which is absolutely appropriate but also fraught with uncertainty.
So the lack of change to our constitutional monarchy is not because we cannot think of how to replace it: it’s because Pierre Elliot Trudeau done goofed.
You're certainly right. It's generally agreed that Canada could become a republic simply by amending the constitution to outline a new law of succession that established a de facto presidency, that would be "heir" to the monarchy, and then advising the Queen to abdicate as Queen of Canada. Then the new head of state inherits the office of the Crown, and is now the President as outlined in law. Elegant, really.
But, politically, the unanimous consent of the provinces to do so is essentially impossible to obtain, due to the history you mention. Canadians also simply don't care much about this. My impression is that most people are basically republicans by sentiment, but their level of actually caring about this is near zero. I'm in that camp myself. I'd like a republic. But the headache of opening up constitutional negotiations? Gah! That has never ended well in our history.
But because the Canadian government rammed the constitution down the throat of the Quebec government, any constitutional change is now a political impossibility. And now Indigenous groups are demanding a seat at any constitutional discussion, which is absolutely appropriate but also fraught with uncertainty.
So the lack of change to our constitutional monarchy is not because we cannot think of how to replace it: it’s because Pierre Elliot Trudeau done goofed.