Canon 1D X II has a 20.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Dual DIGIC 6+ processor. On the other hand, Nikon D5 has a 21.0MP Full frame (35.8 x 23.9 mm ) sized CMOS sensor and features Expeed 5 processor.
Another difference between these two cameras is that Nikon D5's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the 1D X MII and D5 sensor size comparison.
Canon 1D X II and Nikon D5 have almost the same sensor size so none of them has any significant advantage over other in this area.