Panasonic G85 has a 16.0MP Four Thirds
(17.3 x 13 mm ) sized CMOS sensor . On the other hand, Canon R3 has a 24.0MP Full frame
(36 x 24 mm ) sized Stacked CMOS sensor and features Digic X processor.
Canon R3's sensor provides 8MP more than Panasonic G85's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Another difference between these two cameras is that Panasonic G85'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 G85 and R3 sensor size comparison.
As seen above, Canon R3 has a 3.8x Larger sensor area than Panasonic G85. 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.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Panasonic G85 and Canon R3 sensors have been tested by DxO and the results show that R3 has a better overall score of 96, 25 points higher compared to G85's score of 71.