Pentax K-3 III has a
26.0MP APS-C (23 x 15.5 mm ) sized BSI-CMOS sensor and features PRIME V processor. On the other hand, Canon SL3 has a
24.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features DIGIC 8 processor.
Another difference between these two cameras is that Pentax K-3 III's sensor lacks 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 moiré occurring in certain scenes.
Below you can see the K-3 III and SL3 sensor size comparison.
Sensor Size and Resolution Comparison image of Pentax K-3 III and Canon SL3 Cameras
Pentax K-3 III and Canon SL3 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Pentax K-3 III
or the
Canon SL3 ,
including hyperfocal distance.