Nikon D5100, D7000, or a Cannon?

I'm looking into purchasing my first DSLR! I'm really excited, but I'm also wary because this is a HUGE investment. Here's some background information: I would consider myself to be an amateur when it comes to the 'pro' shots, but I'm familiar with the workings of a camera. I'm comfortable operating an SLR camera, and I've had a lot of experience with Nikon D50's, 60's, and 70's (I want to say - not completely positive) since I've taken both film and digital photography classes. I've had some experience with sports photography and I LOVE it (so I would look into purchasing a lens to aid with that), but my real passion is nature photography. I'm traveling to Maui and Australia/New Zealand in a year, which is my real motivation for getting a camera and learning how to operate it right now. I also want to be able to snap nice candids of my family/friends, but I'm not looking to do anything like portraits or special event photography (unless I want to for fun).

I've never shot with a Cannon before, but I've always been happy with Nikon and all of their works. My questions are:
How much more advanced are the 5100 and 7000 when compared to the D60-90 series?
Which brand is the best for DSLR?
And mainly, what are the differences between the 5100 and the 7000? Will purchasing the 5100 make me kick myself in the foot for not hashing out a few hundred more dollars and investing in the 7000?

Brief Summary:
D5000 or 7000
I want a camera that:
takes GREAT nature photos
great shutterspeed options
has potential to dabble in some videos (all for the fun of it)
this camera is for personal use only, but I want clean, crisp, and stunning shots.

These days all cameras will do video full HD and they will all take great crisp shots. You only have to choose. Nikon, Pentax, Canon, Sony, and Olympus make good DSLR's and they all have cameras in various price ranges. You can check out the pentax k30 which just came out and its weathered sealed and gives you the option of using lithium batteries or AA battereies.

Visit this website and check out the DVDs they have, some are just for your camera while others teach you about exposures, lighting, and photoshop.

http://www.quickprocameraguides.com/