I was wondering what, if any, are the technical differences between the two mounting systems. Does one auto focus faster? Can one hold more weight? Things along those lines that make them different.
The Nikon mount is far older than the Canon one. Nikon have updated their old (OLD!) manual focus lens mount continously, adding new mechanical and electronic connections to it over the years to support new features. Canon started with a blank sheet of paper on their EOS mount in the late eighties and did not even try to maintain backwards compatibility. The main difference is that the EOS mount is all-electronic, there is no mechanical linkage whatsoever between camera body and lens. The Nikon mount has a mechanical stopdown linkage and a mechanical autofocus linkage to let an in-camera AF motor drive the AF mechanism in the lens, plus a full set of electronic linkages á la Canon. The consequence is that an old Canon manual-focus lens is now a useless paperweight while any old Nikon manual focus lens can, in principle (there are some gotchas), be mounted and used on the latest and greatest Nikon DSLR.
Also, the Canon mount has a shorter flange distance and a wider opening. The short flange means that there is room for an adapter to fit lenses with other mounts, the wide opening means that making ultra-large aperture lenses like 50mm f/1 and 85mm f/1.2 is possible. Nikon only goes to 50/1.2 and 85/1.4... whether this difference means much in practice is debatable :)
I suppose one of them is screwed clockwise, as usual, and ther other is screwed the other way, counter clockwise. But I don't know for sure, because I use Pentax K-mount...
Seriously, though... they have different flange focal distances:
- Canon EF-S mount, 44.00 mm
- Pentax K mount, 45.46 mm
- Nikon F-mount, 46.50 mm
It means, that through adapters you are can put a Nikon lens on a camera with smaller FFD, but not the other way (with Pentax or Canon lens for Nikon body you cannot focus to the infinity, or you have to use an adapter with corrective optics).
As far as i know they are different just because they were developed at different times, by different companies - other than that both mount do the same job.
Earlier i created question about maximum weight - and we found no clear data about it for both Nikon and Canon. I suspect it depends more on body construction, than on mount itself. As for auto-focus - it depends on lens and camera AF system, not the mount.