Canon 5D MII has a 21.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Digic 4 processor. On the other hand, Canon 5D MIII has a 22.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Digic 5+ processor.
Below you can see the 5D MII and 5D MIII sensor size comparison.
Canon 5D MII and Canon 5D MIII have sensor sizes so they will provide same level of control over the depth of field when used with 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 5D MII and Canon 5D MIII sensors have been tested by DxO and the results show that 5D MIII has a better overall score of 81, 2 points higher compared to 5D MII's score of 79.