By the time you get done with all of your research, there will be a new body out and you'll have to research that too...
Personally, I like Canon.
If this pro that is going to be mentoring you shoots Nikon, I think it would be worth going Nikon just for that reason.
You could (unless he's just an ass) try out his lenses while you're deciding what to get.
He probably has a ton of gear - I would get something that is compatable with it. Not saying that you should try to mooch off of him and always be borrowing crap - but it would be nice to be able to try something out before buying your own.