Both Canon G3 X and Olympus PEN-F have 20.0 MP resolution sensors but Canon G3 X's sensor is 1" (13.2 x 8.8 mm ) and Olympus PEN-F's sensor is Four Thirds (17.3 x 13 mm ).
Since Olympus PEN-F's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Canon G3 X.
Below you can see the G3 X and PEN-F sensor size comparison.
As seen above, Olympus PEN-F has a 1.9x Larger sensor area than Canon G3 X. 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.