Both Canon SL2 and Pentax K-70 have 24.0 MP resolution sensors but Canon SL2's sensor is APS-C (22.3 x 14.9 mm ) and Pentax K-70's sensor is APS-C (23.5 x 15.6 mm ).
Since Pentax K-70'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 Canon SL2.
One other difference between these two cameras that is worth mentioning is that Pentax K-70's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the SL2 and K-70 sensor size comparison.
![Canon SL2 vs Pentax K-70 Sensor Size Comparison]()
Sensor Size and Resolution Comparison image of Canon SL2 and Pentax K-70 Cameras
As seen above, Pentax K-70 has a 1.1x Larger sensor area than Canon SL2. 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.