They're both good cameras and lenses and you'd be hard pushed to notice any difference between them in terms of picture quality.
I've used Nikon all my life, but that's only because I started out with an F2 in 1973. One thing in Nikon's favour is that they haven't changed their lens mount in all that time and I could use the original lens on my current D200, albeit in manual focus mode. The same cannot be said about Canon.
It's really a case of what feels better in your hand.
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