Canon M100 has a
24.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features DIGIC 7 processor. On the other hand, Nikon L820 has a
16.0MP 1/2.3-inch (6.16 x 4.62 mm ) sized BSI-CMOS sensor .
Canon M100's sensor provides 8MP more than Nikon L820's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the M100 and L820 sensor size comparison.
As seen above, Canon M100 has a 11.7x Larger sensor area than Nikon L820. 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.