Ambiguous inquiry in regard to the bodies..
What is the criteria of measurement?? Build? - Ergonomics? - Features? - Sensor design and performance..?
In general I think many people have been conditioned by the media and fanboy websites to think that Canon bodies are not as weather sealed and robust as Nikon bodies, often spreading inaccuracies about models like the 5DmkII such as stating it does not have any weather sealing - which is a load of crap.
When people say that Canon bodies, like the 5DmkII, 5DmkIII and 7D, feel like plastic they are actually referring to the smooth texture of its finish - not the physical build - although few reviewers actually clarify that. As if to assert everyone evaluates build quality by the texture of the paint/finish.... O.o
It is true in many Canon bodies they have designed fewer seals than Nikon bodies, but again few people explain why. In many of Canon's higher-end bodies they implement overlapping seams (like siding is on your house) and therefore do not need the same seals that Nikon uses with butted seams. Canon places seals and o-rings at button points, hotshoe, lcd panels, etc - all those places that one would anticipate seepage.
As for features.. both are equally featured at their price points and equipment tier..
In the area of ergonomics (the ease at which one can control the camera functions) - Canon, hands down. You can access more settings on their higher-end bodies with one hand than you can on any Nikon body, no comparison, period.
Sensor design is the only real difference, and that simply comes down to the different approaches used by each manufacturer. Nikon preferring to have noise be more even, like cheap film and bad exposure produces, versus Canon trying to get rid of it completely, even at the expense of detail loss. Which is the better approach is up to the user - there is no one, right, way. With Canon once you turn off noise reduction you have an easily identifiable noise pattern to process in post, where Nikon has a more uniform noise pattern but is always there no matter what processing you apply. If your output is digital downsamples, or print, then the slight detail loss and splotchy noise pattern of Canon is just not noticeable. If your intended output is crops from full resolution capture, then the granular appearance of Nikon's processing may be preferable.
All in all, I would have to rate Canon as having the better bodies when comparing all aspects, not just porous soft rubber wrappings...
BTW.. Without enabling any type of highlight preservation or in-camera DR features, many of Canon's bodies have greater base dynamic range than Nikon. You can check many different sites around the net - try DPReview for example, where they evaluate/grade the entire operation range of the camera instead of one highest possible single ISO setting performance of a camera like DxO does. Once you do enable DR and exposure preservation features in the cameras the only real difference you see is the manufacturers preference - Nikon increases preservation of shadow detail more than highlights, Canon increases preservation of highlights more than shadows. Again, which is 'better' depends on the photographer. Me personally, when a scene captures my eye and makes me reach for my camera it is specifically the interaction of light and shadow that made it appealing. I am not concerned with nor desire to process out all the shadows, that would completely ruin the imagery of the scene/subject. If I am concerned about anything it is highlights being blown out when wanting to maintain shadows being shadows.. I mean I want the shadows to be just that, shadows. If I could not make out what was in the shadows at the moment of capture, I have no concern with seeing it in the image.
No comparison in lenses. Canon offers a greater selection in their 'pro' lenses than Nikon. Canon offers users the ability to get into pro glass without having to buy the ONLY and most expensive lenses they make like Nikon does. For example (and there are many) the venerable 70-200mm lens you will likely find in any pro's bag, and one most everyone else wants at some point, Canon provides four options from ~$600 to ~$2400, all exceptional optic quality - Nikon has ONE and fork over ~$2400 for it or do not even think about a 70-200m..
Poll