For HD video and snapshots I just picked up a Panasonic TS1. It's submersible to 10 feet and shockproof to a 5 foot drop. Brought it on vaca to Jamaica and it was great for a p&s.
http://1.bp.blogspot.com/_UntK30uX6pY/SkZviu9S_WI/AAAAAAAADg4/ON6Al7ZgtmA/s1600-h/P1000305.JPG
The only cameras that come close to that description are the D90 at 4.5fps and the Pentax K7 at 5.2fps. Keep in mind there is no AF in video mode on the D90. I agree the D300 has the best sports AF of your selections. Before you buy anything, you should evaluate the lens system you're getting into. Canon's lens lineup is the largest and has the fewest gaps as far as I can tell. I have the 17-55/2.8IS, 70-200/4LIS, and I want the 100-400LIS. There are no Nikkor equivalents to those lenses. Someday I will get a 70-200/2.8LIS for indoor sports/theater, which of course Nikkor has one of those. The Nikkor 17-55/2.8, 24-70/2.8, and 70-200/2.8VR are excellent, but cost more than their Canon counterparts, if that matters. The Nikkor 14-24 is outstanding, Canon can't touch this lens.
Choosing between Nikon and Canon is frustrating, because they seem to have agreed not to compete directly against each other's camera bodies. The offerings are quite staggered in spec and price.
The Pentax K7 is weather-sealed (but not weatherproof ) and has in-body IS. Pentax is interesting as they have some neat prime lenses, but they are a small step behind Canon and Nikon at high ISO.
Or if you decide you're not really concerned about HD video in a DSLR and you want to save a few bucks, the Canon 40D is a wonderful camera that can be had for a relative song. I used it and my 70-200 f/4 L IS to take this:
http://4.bp.blogspot.com/_UntK30uX6pY/SNeSm5UP9XI/AAAAAAAAC64/FZHRs6nPCk0/s1600-h/DPP07D80916082303.jpg
And for snowboarding, the first 137 images in this album were taken with my old Canon 30D and that lens:
http://jmphotocraft.smugmug.com/gallery/4484815_z4Kur#263836588_WZpJu