Both Canon SX420 IS and Panasonic ZS70 have 20.0 MP resolution sensors but Canon SX420 IS's sensor is 1/2.3 (6.17 x 4.55 mm ) and Panasonic ZS70's sensor is (1/2. ).
Since Canon SX420 IS'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 Panasonic ZS70.
Below you can see the SX420 IS and ZS70 sensor size comparison.
As seen above, Canon SX420 IS has a infx Larger sensor area than Panasonic ZS70. 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.