Your tripod selection should be based on what you want it to do. For wildlife you will be in the field so weight will be an issue; probably a medium size carbon fiber would be great. If you do night astronomy photography or long exposure (1-30sec) you will need something sturdier and heavier.
Nikon vs Canon? imho an irrelevant issue. Has anyone ever looked at a group of pictures and then identified the camera and lense set that was used to photograph it? NEVER!
And if any post processing was done...more than impossible.
BTW I have a friend who has lots of money and buys whatever he wants. He has all Nikon (DSLRs, V2, P&S and lots of lenses) except for one Fuji 4thirds with lenses and an Olympus something.
So, buy what you want. advice will just confuse you.
The clear winner is ..... the camera you have in your hand when the moment arrives. If anyone could identify the camera used in any of the contest shots you would be more than a genius.
These is professional level photograhy. Are you a professional photographer?
Whatever it is, it is a nice camera!
SUPER! Your photos show your excellent technical skills and creative compositional eye.
I have a friend who loves equipment. Buys whatever he fancies; especially stuff with outstanding reviews. I do not believe he has a complusion. What he has is a lot of money. (Does not bother with eBay; Amazon mostly)
You have a problem only if camera purchses are made with your rent or mortgage payment money.