Not at all compatible on the hot shoe. Different systems. Hot shoe has the large center trigger pin (which is compatible) and a few extra pins (not compatible). The extra pins on the hot shoe are very different between Nikon and Canon. Here is a link that shows the differences: http://www.seacamusa.com/hotshoe-pins.shtml#nikon Guessing, probably there would be no damage, but it cannot work right on the hot shoe.
However, it or any flash should be compatible (in manual mode) on a PC sync cord or with optical or radio trigger. The one caution is that some old flashes have excessively high sync voltage for the PC cord, but that should not be applicable to either the Nikon or Canon speedlights.