I suggest Canon because I like the form factor. For me personally, I have Canon lenses. Also, I have a history with Canon cameras, so I'm slightly biased.
From another standpoint, I don't like the Nikon UI, for whatever reason. It just didn't work for me. As Wingnut said, however, test the camera for yourself. If a camera feels uncomfortable to you, it doesn't matter what lenses are available, what brand it is, etc. You need a camera that fits you.
And I'll refrain from cracking a Harry Potter joke here...(wand/camera choosing wizard/photog)
Welshman: No worries mate! I know how it goes sometimes. I have many friends that shoot Nikon, no doubt they're great cameras. Almost bought a D40 myself when they came out, ended up not buying a DSLR at all, unfortunately.
OH! I don't know if the OP has considered the D40x....? That'd be a more worthy contender, especially considering the price of them online.