listen to what others here have said. it's basically whether you're going with video or photo. Personally, If I was going to leap to Canon and invest in a more expensive body, more lenses and at the same time try to sale my Nikon stuff..I would go for the 5DMKII.
Though I'm not sure about the video from the 5D to 7D.
The question I would ask is "Is $700 really worth it for a little better viewing quality?"
I would say no, and that's the same reason I'm still using my D90.
I'm just waiting for Nikon to release something in the near future that will allow me to keep my lenses while upgrading to a professional body.