this migh be of some interest.
http://www.jimreedphoto.com/content.html?page=5
http://prakashphotography.blogspot.com/2009/02/nikon-d700-vs-canon-5d-mk-ii-weather.html
http://www.luminous-landscape.com/essays/antarctica-2009-worked.shtml
line from this.
The largest group of failures through were among the Canon 5D MKIIs. Of the 26 samples of this camera onboard, one quarter (six) failed at one time or another, and while three recovered, the other three never did. In all cases it appeared to be water or humidity damage. Of particular concern were two cameras which stopped working while completely protected within Kata rain covers during a light rain ashore. They came back to life the following day though and were mostly fine for the rest of the trip, but one died permenently just before the end of our voyage
No Nikon bodies (mostly D700s) failed in any way
Trouble is the 5d mk2 is a studio/portrait/wedding camera
My 5D2 multi-controller (joystick) started playing up in 20 minutes of light drizzle, making it impossible to select the AF point I wanted for certain compositions. Everything was fine once dried out, but I thought the performance was monumentally lame. It strikes me as an utter waste of time to bother sealing anything when such a trivial problem can render the camera all but unusable. Weakest link in the chain etc..
I haven't dared use the 5D2 in anything but the dry ever since. Fortunately I have a 1D3 and 7D for moister conditions, not that I've needed to put either one to the test. I don't want to shoot in the rain.
In keeping with its XD designation, the 7D shares the same extensively-sealed magnesium construction as the 5D Mark II. Canon again claims the same degree of moisture and dust resilience as the EOS-1N pro-level film SLR from the 1990s.
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Fortunately I have a 1D3 and 7D for moister conditions, not that I've needed to put either one to the test. I don't want to shoot in the rain.
The 7D has superior weather sealing to the 5D2? Or would you risk the 7D in wet conditions because it's a cheaper camera?
In both camera bodies, the weather and dust seals have been improved around the battery compartments and memory card doors, and increased precision in the alignment of the magnesium alloy external cover seams and in the optimal design of camera parts and structures contribute to the cameras dust and water resistance. Internal gaskets and sealing materials are used extensively at the cameras buttons, tripod sockets, and surrounding the LCDs. As a result, the EOS 5D Mark II now has dust and water resistance that is almost equal to that of the EOS-1NCanons top-of-the-line professional 35mm SLR for most of the 1990s.
In terms of weather sealing, the EOS 7d features the same level of weather resistance as the old EOS-1N film camera.