I guess that depends on how much cash he'd want for the trade, what kind of lenses you have for a FF camera, your need for the increased ISO performance of FF, and whether you have intentions of upgrading to a new camera any time soon. The 5d2 is a fine camera (providing that one you'd be getting was taken care of - a risk), and theoretically would be 'better' for landscapes - though this will depend on what lenses you have for FF and what kind of light you usually shoot in.
Personal relations aside, I'd have to evaluate if I even want to make the move - if my current camera is coming up short in areas I care about - and then decide if the deal is worth it to me.