Canon R6 II has a
24.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Digic X processor. On the other hand, Nikon Z9 has a
46.0MP Full frame (35.9 x 23.9 mm ) sized Stacked CMOS sensor and features Expeed 7 processor.
Nikon Z9's sensor provides 22MP more than Canon R6 II'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 R6 II and Z9 sensor size comparison.
Sensor Size and Resolution Comparison image of Canon R6 II and Nikon Z9 Cameras
Canon R6 II and Nikon Z9 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 R6 II
or the
Nikon Z9 ,
including hyperfocal distance.