Canon Rumors believes it has information indicating a long-rumored high megapixel R-series camera will come out in the first quarter of the coming year, sporting a 90 megapixel sensor and the ability to take >300 megapixel shots using a version of pixel shift technology.
Pixel shift is the process of using an in-body image stabilization system to precisely move the sensor one pixel over in various directions, taking a shot at each location and stitching the results to make one image with a much higher effective resolution. The figure of greater than 300 megapixels seems roughly right if the Canon version of the technology has a similar effect as see in the Panasonic Lumix S series bodies, which product pictures of 187 megapixels off of a 47 megapixel sensor.
The Lumix cameras are able to process the files in camera (unlike the Sony version of the technology) and tend to do better with images that feature some amount of movement.
Canon Rumors indicates the body will look just like the R5 and R6, not emphasize video performance, and will likely cost about the same as the $3900 R5.