The Canon P and Nikon S2 are not similar cameras. The S2 is similar to the Canon L series, the Canon P is similar to the Nikon S3, the P and S3 both have similar frame lines in the viewfinder.
I have repaired numerous examples of both cameras, and both are similar in quality. The advantage of the Nikon is that it can be wound, focused, and shot with one hand. The advantage od the P is that LTM lenses are more plentiful. That said, the Nikkor lenses are better made than Canon lenses. The lubricant in Canon lenses attacks the coating inside the lenses, first causing haze, and eventually ruining the coating.
The S3 (if you can find one for a good price) is much better than the Canon P. The mechanics are more refined, and the S3 is a smooth operator. I have a couple of S3 cameras, and they are actually smoother and quieter than my Leica M3 or M4 cameras.