Yeah, iirc some of the biggest reasons for including civs like Canada, Brazil, and Australia has to do with there being lots of people from those countries who go "cool, Canada is in? I'm buying it" And choosing civs like the Mapuche or Mali, while possibly more exciting from a geographic or diversity or history context or whatever, may not sell as well. Obviously it's great that they include both in, but I do think that's a large reason why many of the post-colonial civs are more likely to stay around for longer.
Yeah, just because the Queen is on our coins, it doesn't really mean that they have anything really to do with Canada now except for tradition and history. Now, granted, Canada didn't fully gain power over foreign affairs until the 1930s, and didn't fully gain power to modify the constitution without asking England first until the 80s, so in that sense, Canada certainly is a very "New" country in the modern world. There's plenty of debate whether Canada truly has enough history or enough influence to deserve a spot in the game (and as a Canadian, my opinion changes day by day on whether we should be in or not), but we wouldn't deserve to be in the game more if parliament passed a law that declared Harry as the head of state, or if we skipped over that line completely and appointed Wayne Gretzky as the new head of state.