Must qualify this with the Nikon can do 1/500 flash sync using full flash power, and Canon can do 1/250 sync using full flash power. The Canon can do high-speed sync at any speed above 1/250 with a reduced power output, if a strobe capable of high-speed sync is used (like the Canon EX 580, or Sigma 500DG super. I do not know if the Nikon has high-speed sync capability. Someone who is familar with the nikon would need to verify that.
The Nikon has one advantage that it can do flash synchronization up to 1/500th, and the Canon only up to 1/250th. So if you ever want to do a little "fill flash", you're slightly more limited with the Canon.