Where the other Canon cameras tend to come apart in modules (you can take off the back, or take off the front, etc.) the 6D was a bit more interconnected. To get the back off required removing the sides and a bit of the bottom for example. A bit of a pain for the exploring types, but I would imagine it also gives more structural support.
The body is basically plastic, but like most modern plastics it’s thick and solid. Never a thought that a screw was going to strip out during disassembly. Anyway, after a bit the back was off, and looks, from the inside, pretty similar to all the other Canon backs.