Ok so it goes this way
Sam fights John Walker and Bucky fights Lemar Hoskins and Walker kills Sam and Bucky kills Lemar
When the surviving two find out what happened, they're both enraged and want to kill each other.... Bucky goes WS mode and John Walker becomes even more unstable
Who would win the fight?
Note: Bucky has the Vibranium arm and can use the stored Kinetic Energy ability, while John Walker has Captain America's shield in this fight