Considering all the reports of financial issues, I am actually happy to see Nikon release the Z9. On paper, this is an amazing camera, and easily you can see the R1 specs matching it in a year or two. While I've already seen some people emphasizing how much better this is than the R3, to me...we are talking different shades of excellence. If you really need AF 120/sec vs 60/sec, here you go. If you really think you need 45 MP over 24 MP, here you go. If you want 30 fps vs 20 fps, R3. If you want smaller files/less system bandwidth (which Canon continues to say is a market driver), R3.
No doubt both will take many excellent images.