I think the temperate biome is supposed to be the Midwest some where in that general area. They keep saying the campaign takes place in the US but the Taiga map is supposed based on British Columbia which is a province in Canada. So I don't know if they mean the game takes place in the US or North America which would be Canada, United States and Mexico. I don't think there isn't much difference between BC in Canada and the upper North West part of the US. I have have heard people jokingly refer to Saskatchewan as Northern Montana cause they look so similar.
I guess the Alpine part of that map would look kind of like the upper west part of the map in RDR2. I believe it's called Ambarino. Which is kind of based on the area of the US Yellowstone would be in. It's one of my favorite parts the map in RDR2.