What is your real image size?
Ask yourself If the pixel are there why doesn't Cannon deliver large larger images. Like my Cannon 1D4 is listed as a 16.1 MP sensor yet the camera delvers a 15.98 MP image. The pixels are most likely there and used during RAW conversion in or out of camera to produce the best pixels around the images perimeter that can be. Remember sensors do not capture color images. They capture mosaic images which are convert into a RGB image by incorporating information about mosaic color around a pixel to come up with rgb values for a pixel. Perimeter pixels are not surrounded. On top of that lens performance is not as good around the outer parts of its image as it is in the center. When we want a lager field of view we normally change focal length to get it. I would think that if it were worth the effort to increase the field of view using these pixels that Cannon would.