SR,
I have never used Canon, so cannot personally compare. I was an Air Force photographer from 1959 to 1981 and the Air Force always used Nikon (still do and so does the Navy, Coast Guard, and the Marines). I got my first Nikon in 1961 (S3 rangefinder) and have always had the top of the line Nikon. The dynamic range with my D810 was superb and the D850 is even better. I got my D850 around the first of December and have been shooting under all kinds of lighting conditions to see what I can get. I am fortunate in living 100 yards from the Durango & Silverton so have been able to photograph the three times a week Cascade trains as well as the Polar Express trains at night in November and December. It is sometimes difficult to see in a JPEG but the RAW files from the D850 are recording excellent detail in both the highlight and shadows. I do a bit of post processing in Adobe Camera Raw into Photoshop (I do not like Lightroom) and am happy with the results I will be using a lot of my photos in the K-36 and K-28 books I am doing for White River and shadow detail in the black locomotives is a must.
Attached are some samples shot recently, have been shooting back lit scenes, straight on, as well as side lighting and I am satisfied.