Yeah, the Weapon XI is the rumor stuff I had heard involving Deadpool. That he is experimented on, giving him those powers, but I'm not sure if that is confirmed or not. Again, like Bill mentioned, that certainly doesn't look like Ryan Reynolds, and I don't know why they couldn't put the makeup/prostetics on him for these scenes. If it is Deadpool, maybe the extra powers thing is temporary, and he's back to "normal" by the end of the movie and heading towards donning the mask/etc. I know they have hoped of spinning him off into his own movie off of this, so if that works out that may be why he is getting a lot of story/screen time between the various versions.
EDIT: I see in the pics that Dale posted from MTV, that it is indeed a different actor (Scott Adkins) playing "Weapon XI".