Canon S120 has a 12.0MP 1/1.7" (7.44 x 5.58 mm ) sized BSI-CMOS sensor and features Digic 6 processor. On the other hand, Nikon S1200pj has a 14.0MP 1/2.3" (6.17 x 4.55 mm ) sized CCD sensor .
Below you can see the S120 and S1200pj sensor size comparison.
As seen above, Canon S120 has a 1.5x Larger sensor area than Nikon S1200pj. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.