The Nissan workers at Canton MS are mostly African-Americans. They are probably more union-friendly than are the workers in a place like Chattanooga or Spring Hill TN, who are mainly whites. If the Nissan workers vote to install the UAW at the Canton plant, you can bet that other auto manufacturers will take care not to locate new plants in areas of the South that have majority black populations.
In other words, mountain regions yes, cotton belt no.
If the Nissan workers in Canton, MS want a union, Nissan should start moving those jobs to other states.