Canon 80D has a
24.0MP APS-C (22.5 x 15 mm ) sized CMOS sensor and features DIGIC 6 processor. On the other hand, Pentax K-3 III Monochrome has a
26.0MP APS-C (23 x 15.5 mm ) sized CMOS sensor and features PRIME V processor.
One other difference between these two cameras that is worth mentioning is that Pentax K-3 III Monochrome'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 moiré occurring in certain scenes.
Below you can see the 80D and K-3 III Monochrome sensor size comparison.
Canon 80D and Pentax K-3 III Monochrome 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.