Chris Clarke , Feb 19, 2010; 02:46 p.m.
I didn't know Canon made such a focal length. I think you are talking about a Tokina or Sigma lens, both of which are made for a Canon EF-S mount.
The Canon EF-S 10-22 lens is obviously an EF-S lens and won't physically fit on a FF camera. Only EF mount lenses will fit the 5D2. I have the 16-35 II which is wider on a FF than a 12-24 is on a 1.6 crop.
There are plenty of options on FF for a new lens to fill the gap left by your 12-24.