Well it just seems that you would want to use the same brand due to compatibility.. I have a d90. Go to the store and try holding it out. Maybe you will like it... or the d300s.
Did you try the Sony in person as well? Ideally, you would be able to have the Canon, Sony, and any potential Nikons (like the ones Boogschd mentioned) right there to fiddle around with and try out. That said, if you've tried them and the cameras seem pretty much equal in terms of comfort and ease of use, I would go for the Canon because there would be a larger variety of lenses and gear available compared to Sony. I don't have personal experience with either of those cameras, though, so that's about as much info as I can offer.
Good Sony lenses are quite a bit more expensive than Canon, load of top quality secondhand Canon lenses but not many Sony, but it all depends on what you shoot,also one is full Frame and the other 1.6 crop
May I ask why you need to upgrade? Is it the current camera cannot do what you like to do? It maybe helpful for us to give you advice if we know what feature(s) you are going after.