I have a feeling it's gonna take place or parts of it will take place in Wyoming-
The river we saw at the start of the trailer looks very synonymous to Snake River, Wyoming
I understand a lot of rivers meander like this, but the topographical features and the surrounding nature are really quite similar.
Snake River Wyoming with the Tetons in the background-
Red Dead Redemption 2 Trailer Screencap
These mountains; the Tetons, Wyoming also remind me a bit of the Three Peaks. Also guess what? the Tetons were originally named by French settlers; 'les tois tetons', meaning the three nipples like three peaks.
This mountain here, Mount Robson, British Columbia.
Looks similar one of the many mountains that one we see on the right at the end of the Red Dead trailer.
Part of the Rockies so I have no doubt that those are the Rockies towards the end.
I believe Chinese Takeout has the right directions on his panorama compass.
I think our map will be located just East of the Rockies, so I would expect places like Wyoming, Colorado, South Dakota, Nebraska.