Generally its not worth switching systems.. Too bad you already sold some gear before you asked.. :-( If I were you, since you do not seem to know exactly why you are switching I would stay with canon. Wait till you know exactly what the new gear will do for you before deciding to leap. However, like the others said.. Nikon is the best for photography. and canon has the edge for video though nikon is catching up. Also the Nikon Flash system aka the CLS is a huge plus for nikon users. I know people who switched system to nikon Just for the CLS! But if you dont use strobes often Its pointless.. . The point is know what you want from the system. Then match it against the features of your current system and compare it with teh features of the system you intend to switch to.
Good luck with your decision.