I know that so many men, so many minds, I know how hawkish the users of the both systems are set against each other, but I let myself speak out on this point. Moreover, recently the new aspects appear, due to a release of new cameras.

The both manufacturers, Canon so Nikon produce excellent DSLR cameras, which provide fantastic image quality, and similar features. As there are so many similarities between the brands, many people think that it does not matter which brand you eventually choose. I believe, that in the skillful hands of any one of them will show excellent results, but there are significant differences between these two brands, which may affect your decision which camera to buy.

Advantages of Nikon cameras

Good quality in low light conditions. Over the past two years it turned out that very few people would argue, the Nikon has excellent quality in low light conditions than comparable Canon cameras.
Number of AF points. Most people would agree with me, most Nikon cameras have more AF points than their Canon counterparts. When you hold the camera in hands, you'll see how important this is. Sometimes the low number of AF points in Canon cameras does not allow to focus where you want, forcing a photographer to change the point of focus, and then the composition.
Flash control. Until late Nikon was in the lead, but today Canon overtakes it on this parameter.
Larger APS-C sensor. Nikon uses in its cameras a larger image sensor, what even with a smaller number of pixels provides a more accurate picture. This applies to crop frame cameras. For Nikon DSLR these are reflex cameras apart from D3, D3S, D3X, D4, D700 and D800; For Canon these are models EOS 600D, Canon EOS 550D, 500D, 1000D, 450D, 400D, 350D, 300D, 60D, 50D, 40D, 30D, 20Da, 20D, 10D, 7D, D60, D30.
Attention to small details. It is believed that Nikon is more friendly, in the sense of extras and the presence of pleasing little things in the camera.

Advantages of Canon cameras

Video. Almost all the best videos on Vimeo, filmed with the Canon. Nikon begins to gain popularity with 1080p video and a good autofocus system in the latest models but still has significantly fallen behind Canon in this aspect of the. Canon DSLR offers larger frame rate.
Price. Nikon cameras and lenses are often a bit more expensive than those from Canon. Obviously, there are exceptions, but if you look at the range of digital reflex cameras and popular lenses, the Nikon usually cost about 8-10% more than comparable Canon. I think due to the difference in price a greater number of people use Canon.
The number of megapixels. Most photographers are paying great importance to this aspect because it is convenient to be able to work with more significant amount of megapixels. Canon goes slightly ahead regarding the number of pixels.
Availability. When Canon announces a new camera, you can expect to get it in the shortest time. When Nikon announces the release of a new camera or lens (especially the more expensive models), it often takes from 4 to 6 months.
Motor. All contemporary Canon lenses have built-in motors. It a little bit different with Nikon, and may later you will have to pay the extra money for a lens with a motor; also lenses don't always fit the cameras.

In Conclusion

Canon is a much more global company than the Nikon. Canon produces printers, cameras, video equipment, binoculars, calculators and more. Nikon is a company with an entirely different approach to business. It focuses almost exclusively on the cameras (although they do sport optics and scanners). This factor does not give any of them additional advantages but points to the difference in the business approaches of the two corporations. Canon may have an advantage due to greater resources, considering the size and the possibility of a huge company. Nikon may have an advantage since they are focused on the one main product, and do not scatter their talents on trifles.