Nikon Z7 has a 46.0MP Full frame (35.9 x 23.9 mm ) sized BSI-CMOS sensor and features Expeed 6 processor. On the other hand, Canon R has a 30.0MP Full frame (36 x 24 mm ) sized CMOS sensor . Nikon Z7's sensor provides 16MP more than Canon R'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 Z7 and R sensor size comparison.
Nikon Z7 and Canon R have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.