It is Canon 60D, not D60. Canon naming is numberD, Nikon naming is Dnumber.
Here is a Nikon D60.
http://www.dpreview.com/reviews/nikond60/To capture your dog running, and sports such as a football players running for example, all you need is a shutter speed of around 1/1000. Anything faster than that is probably not necessary. Even if you double the shutter speed to 1/2000 that will be plenty fast enough.
The faster maximum shutter speed is more for the case when it is sunny outside and you are using a fast lens with a wide aperture for a shallow depth of field effect. Fast being f/2.0 and faster. The faster shutter speed will prevent over exposure.
Maximum shutter speed will not be an issue for you. The more important value when shooting action is the number of frames per second. 7D fps > 60D fps, but the 60D fps is likely good enough. You will need to look up the actual values.
Comparing the 7D to the 60D, the 7D has faster fps, better auto-focus system, more auto-focus points, plus other features. 7D also uses the more expensive and faster CompactFlash cards, vs the 60D using SDHC cards. If you plan to shoot sports, get the 7D. If plan to occasionally shoot your dog, the 60D will be fast enough. The articulating screen on the 60D will also be very useful for shooting macro and video.
It would also be better to get the 60D and some better/faster lenses than the 7D and some average variable-aperture lenses.
Nikon Coolpix P100 - It is a point and shoot camera, forget about it.
Nikon D5000 - I don't know much about this model, but it is newer than the D90.
Nikon D90 - Is Nikon's first attempt at DSLR video. 720P maximum I think. Video is not it's strength if that is important to you.
Sigma does make a 17-50 2.8 lens for Canon (someone above said that he could not find it) .
Sigma 17-50mm F2.8 EX DC OS HSM Zoom Lens for Canon DSLRs with APS-C Sensors
http://www.bhphotovideo.com/c/product/689620-REG/Sigma_583101_17_50mm_F2_8_EX_DC.htmlAnother thing to keep in mind is that using a DSLR for video pretty much means that you will need to manual focus the lens. You can't just point and shoot the video and expect good results. The people that are using DSLR for video do a lot of post processing and editing. If you want to just point and record video, a digital camcorder that will provide continuous autofocus will give you better results. DSLR may offer excellent image quality in the video, but if the image is not in focus, that excellent image quality doesn't mean much.
The Nikon D7000 has continuous autofocus in video mode, but it does not get the correct focus all the time. There are video reviews of the D7000 continuous autofocus available on youtube that show this.
The most popular places to buy DSLR cameras for the lowest price is probably one of:
http://www.bhphotovideo.com/http://www.adorama.com/http://www.amazon.com/