Both Nikon P300 and Canon S100 have 12.0 MP resolution sensors but Nikon P300's sensor is 1/2.3-inch (6.17 x 4.55 mm ) and Canon S100's sensor is 1/1.7-inch (7.44 x 5.58 mm ).
Since Canon S100's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Nikon P300.
Below you can see the P300 and S100 sensor size comparison.
As seen above, Canon S100 has a 1.5x Larger sensor area than Nikon P300. 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.