Leica S2 has a 38.0MP Medium format (45 x 30 mm ) sized CCD sensor . On the other hand, Canon 5DS R has a 51.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Dual DIGIC 6 processor.
Canon 5DS R's sensor provides 13MP more than Leica S2'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.
One other difference between these two cameras that is worth mentioning is that Canon 5DS R'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 moire occurring in certain scenes.
Below you can see the S2 and 5DS R sensor size comparison.
As seen above, Leica S2 has a 1.6x Larger sensor area than Canon 5DS R. 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. Leica S2 and Canon 5DS R sensors have been tested by DxO and the results show that 5DS R has a better overall score of 86, 10 points higher compared to S2's score of 76.