Looks like we will play Arthur Morgan:
Rockstar has released a new trailer for Red Dead Redemption 2. It reveals the first official details about the game’s story, which will be a prequel, and star a new character, Arthur Morgan - not John Marston.
Rockstar describes the game as “the story of outlaw Arthur Morgan and the Van der Linde gang as they rob, fight and steal their way across the vast and rugged heart of America in order to survive.”
The Van der Linde gang is also known as Dutch’s Gang, which the last game’s protagonist, John Marston would eventually join (and leave).