There has always been 2 things differentiating Canon and Nikon in the digital world. first of all is image sensor size. Canon has always had a full sized image sensor for recording the image (full framed = sized the same as 35mm film). Nikon has always argued that you can slightly reduce the size, still fit the exact same amount of information/quality of image, and save costs all around. A lot of people switched to Canon because Nikon didn't have a full framed version to show as a comparison, and people just thought the bigger sensor must be better.
Nikon recently came out with a full frame sensor (FX-CMOS) in their newest, highest end camera, the D3 and D3x (costing over $5k). Many Canon enthusiasts have even sid that this is now the best camera on the market, even better than their Canons. BUT, truth be told...when looking at images taken under the exact same lighting conditions, of the exact same subject, with the exact same camera and lens, there is zero difference between image quality, clarity, color, sharpness, or apparent depth of field between the two Nikon sensors. So it appears Nikon was correct in their stance.
But a lot of photographer's still have/use Canon. Impart to there was no full frame Nikon for comparison until very recently, so people aren't going to switch over $15k worth of gear (camera body and lenses) over night, so they're sticking with their Canons. The other thing, most pertinent to Sports and Action Sports Photography, especially on the lower end/recreational and enthusiast level cameras, Nikon cannot compete wiith Canon in their power drive. The amature/enthusiast level cameras from Canon can continuously shoot 6 frames per second, where as the Nikon can only shoot 3 frames per second. Thats a big difference in action sports. At the upper levels the two camera brands are the same, but then you're spending $3-5k.
So, even though I'm a Nikon guy, for a non-pro photographer looking to do action sports, I'd say go with a Canon. If you were looking to do nature, wildlife, landscapes, etc. and some sports, I'd say the Nikon for sure. But being that you'll be doing skiing and the like, the Canon's power drive will be your biggest advantage.
OK, so actual cameras... Both companies have recently renamed a bunch of their models. They never seem to make thinks easy.
The "cheap" cameras by Canon are around $500. Those are the most basic level cameras they make (Canon EOS Rebel XS). They shoot only 3.5 frames per second. Nikon's equivalent is the D40, and shoots 2.5 frames per second.
Next level up is a broader price range, about $600-$1000. Canon has the EOS Rebel XSi (slightly tweaked version of the one above) and their EOS Rebel T1i (3.4 frames per second). Same price range, Nikon has a new group of cameras just out within the past 2 months (the D3000 and D5000), which have 4 frames per second- so actaully faster than the lower end Canons! At this price range Nikon also has the slightly older D60 (been around for a year and a half), with 3 frames per second.
After that I'd say is the $1000-$1400 range. That puts you into the range that has the biggest difference in power drive and largest advantage for Canon. This is also the level that most camera enthusiasts really start their comparisions between the brands on, as these are the most basic level cameras you would use on an advanced amature/beginning pro to try and sell images from. Does that mean the others are really that much worse? No. But magazine editors and such don't really look at images produced by cameras on the levels lower than this for some stupid reason. For Canon you'd be looking at the EOS 40D, and it has 6.5 frames per second! And though it has less megapixels than the T1i (the 40D has 10.1mp as opposed to 15.1mp on the cheaper T1i, but the lower mp 40D actually has BETTER image quality). The equivalent on this level for Nikon is the D90. A fantastic camera, however it only has 3 frames per second...half that of Canon.
In the end it really all comes down to personal choice. If you're looking to spend upwards of $1400, but not higher, go with the Canon. It pains me to say it, but its the truth. The power drive will make the biggest difference. If you're looking at one of the less expensive cameras, then there's truthfully no difference. At the lessor price ranges, the Canons will usually have a higher megapixel count, but with the image sensors used on those "lower end" cameras, a higher megapixel count won't always result in a better quality image, it can actually make it seem worse. So, if you're going for one of the two lower cost ranges of cameras, it basically comes down to two things: 1) do you already have lenses for one brand versus the other; 2) which user interface do you like using better?
Same thing with the higher end...in my opinion. Power drive speed balances out again. Again, there truely seems to be no visual difference between Nikon's DX-CMOS sensor versus their newest FX-CMOS sensor...and the images are as good as the Cannon full frame sensor...so the old issue between higher end Canons being than Nikon for the true full sensor argument is holding less water. So what cache of lenses do you already have? Which interface are you more familiar with/prefer? There's your answer.