The only really significant difference between the two brands is that Nikon are committed to their 1.5X crop format across their whole range and have no intention of going any larger, while Canon offer 1.6X, 1.3X and full frame, with the latter coming down fast in price and sure to be going 'mainstream' before too long. If full frame is a serious consideration for you in the future, then it would make sense to change to Canon but you would also need to start choosing your lenses carefully to get the best out of full frame, and it means expensive glass!
Apart from that you're not going to see any significant difference in your results whether it's a Nikon or a Canon.