History of abolishing the monarchy

The government of Barbados  -- an independent country since 1966 -- has announced it will move forward with plans to abolish the monarchy and replace Queen Elizabeth II with a Bajan [apparently it is:] Barbadian head of state:

Barbados has decided to press ahead with long-running plans to remove the Queen as head of state, prompting speculation that other Caribbean islands may follow suit in the wake of the Windrush scandal* and the Black Lives Matter Movement.

Barbados said it intended to become a republic by November 2021. The move requires a two-thirds majority in parliament, and there are no plans to have a referendum, something that is not required in the constitution but had been previously proposed.

News reports do not dwell on how Barbados will choose its head of state in its new republican mode.

There are Canadian experts who have declared it is impossible to abolish the monarchy in Canada, because the Crown is so inextricably bound into the Canadian constitutional system. I guess Barbados's legal drafters must be a lot smarter than ours. They seem to foresee no great difficulty.

It is true that the Canadian federal system would create complexities in abolition that a unitary state like Barbados does not face. Unanimous consent from the provincial and federal parliaments would be required, for one thing.  But with political agreement secured, the processes should not be insuperably difficult.   

* The Windrush scandal arose from the British government's 2018 declaration that British subjects from the Caribbean who had settled in Britain -- as far back as the voyage of the Empire Windrush in 1948 -- were actually not British citizens and could be denied benefits of citizenship and even deported back to the Caribbean.

Update, September 24: Helen Webberly comments.

Thank goodness I have never heard experts, from Canada or elsewhere, declare it is impossible to abolish the monarchy because the Crown is so inextricably bound into the constitutional systems of old British colonies. And I wouldn’t believe it anyhow

In Australia, for example, we had a referendum in 1999 about ending the monarchy here and there was no majority for Yes in any Australian State. The referendum will be run again one day in the future and this time, I am sure, we will vote that Australia should become a republic.

Nonetheless the big question remains for many Commonwealth countries. If we lose the monarchy, what will replace it? A politician that opposes Parliament, like the USA? A figurehead governor general who receives ambassadors and opens ANZAC parades?

(Actually, a "figurehead" Governor-General sounds pretty good to me. Declare the Canadian throne vacant, confirm the GG as head of state, confirm a selection process, leave everything else alone.)