I don't think we need new Colonial Regions. What's more, actually colonial regions are not even necessary anymore imo.
Why? This colonial region would only exist to cater for Acadia, for every other country it would be of neglectable importance. Similarly there shouldn't be a Cuba colonial region, for example.
We could simply tie different colonial countries (and their cultures) to different regions/areas. This would help us to have more and nicer colonial nations.
The current setup works for Brazil and Mexico, because those make up a colonial region in themselves. But for smaller countries there could be more specific requirements, for example the aforementioned Acadia could be formed if it's in Acadia region, and Acadian culture could spawn if it was French, while let's say Cuba requires Cuba itself (and maybe Puerto Rico) as a base, and Iberian culture group to spawn Cuban culture.
For other countries, generic tags would remain like British Canada and Portuguese Caribbean, if they colonize these regions first.
This solution could help other smaller countries to come to life, like Texas or Chile, for example.
Regarding British Canadians I mostly share your view, but let me elaborate it.
What if there was a unified British culture added to the game?
Most of England, Scotland and Ireland always have identified themselves primarily as such and secondarily as British, in case they were "royalists". So it's accurate to have Scottish, English, Irish etc... but what if with the formation of Great Britain the primary culture would become British, with this culture appearing in London, a bit like when Prussia is formed and Berlin turns Prussian. Since GB is an Empire, English, Welsh and Scottish would be instantly accepted, and colonies then would be British instead of English, which is great for later-game targets like Canada and Australia. It could also represent the royalists of (N.) Ireland.
I know this is 21th century, but 18th century could be very similar (probably with darker Wales):
Sorry for hijacking the topic a bit, but in North America French and British history is really interconnected, so I think it's kinda fine.
Like this, an accurate Canada in Eu4 could be achieved, with British instead of English, Acadian in case France colonizes Acadia, and additionally Quebecois might spawn in Francien provinces there.