Sony A7 V has a
33.0MP Full frame (35.8 x 23.8 mm ) sized Partially-Stacked CMOS sensor and features Bionz XR2 processor. 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.
Sony A7 V's sensor provides 13MP 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.
Another difference between these two cameras is that Sony A7 V's sensor lacks 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 moiré occurring in certain scenes.
Below you can see the A7 V and 1D X MIII sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A7 V and Canon 1D X III Cameras
Sony A7 V and Canon 1D X III 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
Sony A7 V
or the
Canon 1D X III ,
including hyperfocal distance.