There's a nice burn on the X-Men Origins: Wolverine
version of Deadpool in the preview trailer:https://www.youtube.com/watch?v=QPZHBjyUGhQ
Both characters are played by Reynolds. And given that Deadpool has the unique superpower of knowing he's a character in a comic book (and we assume, a movie), and routinely breaks the fourth wall, it has the potential to get ridiculously meta.
I think you could probably reason with the time travel stuff that went on in Days of Future Past
that the Weapon X program that developed Wolverine and Deadpool in Origins
never existed. As I understand it, Deadpool does exist in the Fox X-Universe.