Canon G7 X MIII has a 20.0MP 1-inch (13.2 x 8.8 mm ) sized BSI-CMOS sensor and features DIGIC 8 processor. On the other hand, Ricoh GR III has a 24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor .
One other difference between these two cameras that is worth mentioning is that Ricoh GR III'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 G7 X MIII and GR III sensor size comparison.
As seen above, Ricoh GR III has a 3.2x Larger sensor area than Canon G7 X MIII. 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.