The 550D CR2 raw format is indeed 14-bits per pixel (i.e. 0 – 16384) but the processing for extracting the green channel from the two green pixels of Bayer colour array adds an arbitrary scaling probably due to the interpolation required. A simple scaling doesn’t really matter since you do the photometric calibration after extracting the green channel.
Most of the non-Canon software in use uses functions based on dcraw to do this coversion so you can have a look at the source code if you are interested!