Takes place in Metropolis. Superman is not completely invulnerable anymore (he can be killed from enough force and without kryptonite). Deadpool is just Deadpool, and he has all of his powers and weapons. I'm not going to bother asking about the comic versions fighting the movie versions, because comic versions are OP.
I'm saying that he is not immune to injury. I'll say that "enough force" is really what it would take to kill him when he is being poisoned by kryptonite, if that makes any sense.
It doesn't since he's shown different levels of resistant to Kryptonite in different cases. Like at one point a small piece of it will bring him to near death but other times he'll be able to function(abiet weakly) around larger pieces like Metallo's heart.