Basically the same scenario as the movie but with one twist.
Cable is the augmented human sent back in time to find Dani and protect her from the Rev-9 that's coming for her. Realizing that he may need help, Cable calls in Deadpool for back up. After a long conversation filled with jokes about who the hell is directing this train mess and some awkward groping, Deadpool finally agrees.
This is film versions all around obviously. Can Cable and Deadpool put the Rev-9 down.