Interesting discussion. I think there are a few points to it.
First of all - Canon has a major advantage above Nikon and Sony and any other SLR manufacturer and that is the lens lineup. I mean, endless choices, superb IQ etc etc.
The major disadvantage of Canon against Nikon, Sony etc. is the sensor technology. Look at the scores of all the Canon sensors and compare them to the Sony sensors which are now in more than 60% of all cameras worldwide and you will realize that Canon sensor tech blows. If Canon would have the Sony sensor inside, it would immediately become the king of the hill. Sony sensors and Canon lenses would be an unbelievable combination which would be unmatched. But perhaps that is the reason why Canon so far has no access to them.
Then, Canon has an other major issue and that is inovation. In the mirrorless segment they are too late, and what they presented is less than what you get with the competition. Sony is rolling through this segment with their NEX line and neither Nikon nor Canon will be successfull there.
And while many will dislike what Sony is doing, the SLT is a great evolution, the A99 will bring video features which benefit from the Sony Pro Video experience, they release an affordable FF NEX video camera, the FF RX1 etc. And while Nikon at least benefits from the Sony sensors, it seems Canon is stuck somewhere behind with not so many product novelties coming out, while the Nikon/Sony dynamic duo is pushing forward.
There is one more thing to add where Canon should watch out. Sony is pushing agressively forward. While the partnership with Hasselblad right now only produced a looney camera at an incredible price, it will in the future help promote the E and A mount Sony uses. Sony has also purchased a major stake in Olympus, so it IMHO is only a matter of time when we will see the first Olympus A or E mount camera. Again, Canon must move finally and improove or outsource their sensor tech. Otherwise they will get eaten by Nikon/Sony.