Leica S2 has a 38.0MP Medium format (45 x 30 mm ) sized CCD sensor . On the other hand, Canon 1D X III has a 20.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Digic X processor.
Leica S2's sensor provides 18MP more than Canon 1D X III'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.
Below you can see the S2 and 1D X MIII sensor size comparison.
![Leica S2 vs Canon 1D X III Sensor Size Comparison]()
Sensor Size and Resolution Comparison image of Leica S2 and Canon 1D X III Cameras
As seen above, Leica S2 has a 1.6x Larger sensor area than Canon 1D X III. 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.