Just like the EOS-1D/1Ds/1V the Mark II is fully environmentally sealed, this means that there are rubber O-rings around the controls and that compartment doors have rubber seals. In total the camera has no less than 90 environmental seal points (indicated in red in the image above). It is however worth bearing in mind that the camera is only as well sealed as the lens used, and for that you'll need one of the special L lenses with rubber grommets which fit flush to the lens mount:
* Canon EF 16 - 35 mm F2.8L USM
* Canon EF 17 - 40 mm F4.0L USM
* Canon EF 24 - 70 mm F2.8L USM
* Canon EF 28 - 300 mm F3.5 - F5.6L IS USM
* Canon EF 70 - 200 mm F2.8L IS USM
* Canon EF 300 mm F2.8L IS USM
* Canon EF 400 mm F2.8L IS USM
* Canon EF 400 mm F4.0 DO IS USM
* Canon EF 500 mm F4.0L IS USM
* Canon EF 600 mm F4.0L IS USM
* Canon Extender EF 1.4x II
* Canon Extender EF 2.0x II