Canon 1Ds has a
11.0MP Full frame (35.8 x 23.8 mm ) sized CMOS sensor . On the other hand, Canon 1D C has a
18.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Dual Digic 5+ processor.
Canon 1D C's sensor provides 7MP more than Canon 1Ds'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 1Ds and 1D C sensor size comparison.
Canon 1Ds and Canon 1D C have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.