Both Canon 7D MII and Olympus E-M1 II have 20.0 MP resolution sensors but Canon 7D MII's sensor is APS-C (22.4 x 15 mm ) and Olympus E-M1 II's sensor is Four Thirds (17.4 x 13 mm ).
Since Canon 7D MII'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 Olympus E-M1 II.
Below you can see the 7D MII and E-M1 II sensor size comparison.
As seen above, Canon 7D MII has a 1.5x Larger sensor area than Olympus E-M1 II. 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. Canon 7D MII and Olympus E-M1 II sensors have been tested by DxO and the results show that E-M1 II has a better overall score of 80, 10 points higher compared to 7D MII's score of 70.