Canon 1D C has a
18.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Dual Digic 5+ processor. On the other hand, Canon 6D MII has a
26.0MP Full frame (35.9 x 24 mm ) sized CMOS sensor and features DIGIC 7 processor.
Canon 6D MII's sensor provides 8MP more than Canon 1D C'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 1D C and 6D MII sensor size comparison.
Sensor Size and Resolution Comparison image of Canon 1D C and Canon 6D MII Cameras
Canon 1D C and Canon 6D MII 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.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Canon 1D C
or the
Canon 6D MII ,
including hyperfocal distance.