Nikon P7100 has a 10.0MP 1/1.7" (7.44 x 5.58 mm ) sized CCD sensor and features Expeed C2 processor. On the other hand, Canon S120 has a 12.0MP 1/1.7" (7.44 x 5.58 mm ) sized BSI-CMOS sensor and features Digic 6 processor.
Below you can see the P7100 and S120 sensor size comparison.
Nikon P7100 and Canon S120 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Nikon P7100 has 20% larger pixel area compared to Canon S120, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.