Hi,
You 5D is a roughly 12 MP camera. The raw file (CR2) contains the raw information of 6 mp green-filtered pixels, 3 mp of red-filtered pixels and 3 mp of blue-filtered pixels. Search for Bayer pattern to see a schematic of the typical pixel array on your sensor. The raw converter (ACR, LR, DPP, etc,) de-mosaics that raw data into a roughly 36 mp RGB file. The algorithm used to transform the raw data into a full RGB file is black magic to this chemical days photographer. It used to be that photography was a combination of physics, chemistry and magic, now it is physics, statistics and magic!
Jean-Michel