An interesting fact... Nikon has had the same lens mount system since 1959. Canon pissed all the Canon pros off and changed to the current mount system in 1987. Notice that the diameter of the mount on the canon is larger. That may be why canon has more super wide open aperture lenses than Nikon. Canon has had a history of having better autofocus but the latest Nikon's are just as good from what I've read.
The Nikon lens mount has stayed the same, but the technology and drive system has completely changed.
Around five or six years ago a huge number of wedding photographers left Canon for Nikon primarily because of focus issue with Canon, myself included, plus Nikons much better ISO performance at the time. Canon AF was better for sports and anything moving much, but for everything else Nikon was better. I really hope Canon has improved, I had a shockingly bad run with Canon that cleared up as soon as I switched.
These days they're probably pretty much equivalent. I'm still wary of Canon AF issues though, especially with how poor CPS was back then.