Lady Bird star Tracy Letts and Fargo actress Rachel Blanchard are set to join Ben Affleck and Ana de Armas in Adrian Lyne’s erotic thriller Deep Water over at New Regency, Collider has exclusively learned. As we reported back in August, Deep Water finds Affleck and rising star de Armas playing a married couple who open up their marriage in the hopes of saving their relationship, only to see things take a dark and deadly turn. Details on Letts and Blanchard's characters are under wraps, but it's believed that Blanchard is either playing a woman who has …