hello. i do a lot of numismatic photography. micro-photos >< so i have searched extensively for the just right camera and acessories.
1. copy stand for still photography - must have with optional lighting attatchments
2. live image viewing - never actually have to take a photo if used with a screen shot software - saves time and reduced the TIFF file size while maintaining high-quality dpi
3. get an ac adapter so never have batteries die if you do a lot of in-house imagry
4. a remote is a nice extra so to reduce even the slightest of movement
5. tilt-lens , optional extra depending on how specific your photography is
6. add-on micro lens combinations - still have yet to figure out the best ones for this but +4 52mm seems to be best for coins - zoom in a lot and move camera back a lot
i think with canon and nikon you will be splitting hairs, both are known for supreme photographic quality. so it boils down to specific needs and optional equiptment prices beucase the accessories from one company to the next can sometimes have a 50% difference.
one last thing, above all else, knowing photography and your camera extensively makes up for a lot and even the average camera with a decent 5-7.2 megapixel will bring the same photo quality. im using an old sony hand-held cyber-shot 5.0 megapix and my photos will smoke 90% of the ones you see on ebay, for coins and it is several years old. it is all about staging. ;-)
so after all that to re-itterate, the canon vs the nikon is simply a matter of preference
have fun !