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, Sony A7R II has a 42.0MP Full frame (35.9 x 24 mm ) sized BSI-CMOS sensor and features Bionz X processor.
Another difference between these two cameras is that Sony A7R II'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 moire occurring in certain scenes.
Below you can see the Z7 and A7R II sensor size comparison.
Nikon Z7 and Sony A7R II 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.