There are a few things that would lead me to the D500 over the 7D II for wildlife/action.
First is that the sensor performance of the D500 is much better. It has better ISO performance, greater dynamic range, and it is very nearly ISO invariant. These things matter when light levels drop (wildlife is most active early/late), and when you have really tough situations like a black and white bird (or uniforms) in strong sunlight.
The Nikon also has a 153pt AF system with focus points that go nearly to the very edge of the FOV. It also has a bit better f/8 AF functionality. IMO, these are relatively small differences that will only affect limited situations... but it shouldn't be surprising how often many end up at f/8 with TC's when photographing wildlife.
Lens choices are a bit harder, but if staying brand specific I think Canon has a few more/better options (my current wildlife zoom lens of choice is the Sigma 60-600).
This is a Hooded Merganser I photographed in hard light... I underexposed the image by about 3 stops in order to retain details in the white feather regions and recovered the rest in post. IDT you could get anywhere near the same kind of results from the 7D II (or perhaps any current Canon model).
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