The answer really depends on your budget. I don't really know Nikon but all the newer Canon bodies and I'm assuming the Nikons will have HD video capability. For motorsports you really can't beat the shooting speed and cost efficiency of a middle-end crop body camera - meaning you'll want the Canon 7D or Nikon's comparable.
Lens selection: the 70-200 2.8 IS/VR has the perfect reach for shooting drifting at just about every track I've been to, and the stabilization feature will really help on the panning shots. That said, this will be one of the more expensive lenses in either manufacturer's line-up. However, this is what I use for 95% of my photos, so I'm definitely squeezing the worth out of it.
Whatever you decide on check between http://www.bhphotovideo.com/
for the best price. Nobody has these two beat in both price and credibility. B&H is typically cheaper or the same as amazon (though you'll sometimes find the odd item cheaper on amazon) but it's nice to have a retail location you can walk into if there are any problems. If you take the train into Penn Station B&H is located right there - the store is ridiculous. If you have the time to go into the city it's worth stopping in and they'll be able to let you play with everything you're looking to buy.