Canon G5 X MII has a
20.0MP 1″ (13.2 x 8.8 mm ) sized Stacked BSI-CMOS sensor and features DIGIC 8 processor. On the other hand, Nikon D7500 has a
21.0MP APS-C (23.5 x 15.7 mm ) sized CMOS sensor and features Expeed 5 processor.
One other difference between these two cameras that is worth mentioning is that Nikon D7500'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 G5 X MII and D7500 sensor size comparison.
As seen above, Nikon D7500 has a 3.2x Larger sensor area than Canon G5 X MII. 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.