I'm perplexed by the Nikon D200 suggestions seeing that your primary focus is landscapes. I own a 5D that was purchased specifically for landscapes (including stitched panos), fine art images and to a lesser degree, wildlife images. I can't imagine going for the less than full frame sensor and fewer pixels offered by the D200 if you want big, detailed landscapes. The image quality of the 5d is truly outstanding - the camera is, to me, worth every penny.
My personnal view is that:
- the D200 will have more DoF thanks to its smaller sensor, which is key for landscape,
- the more uniform image quality you get from using DX lenses on an APS sensor helps getting very high quality stitches,
- the DX lenses like the 12-24 are typically lighter and smaller than the equivalenet Canon 16-35 or 17-40, which is important for backpacking,
- the APS sensor will make your long lenses behave like if they were 1.5 times longer, meaning that a 200-400 AF-S VR on a D200 will cover everything from 300 to 600 mm at a fraction of the cost and weight. This is a huge plus for wildlife, enough by itself to justify buying an APS body IMHO,
- the D200 is more rugged than the 5D, and this might or might not be important depending on your type of shooting,
- low light AF appears to be more reliable and accurate on the D200, which helps for all these pre-dawn images where it is hard to manual focus,
- the price is much lower,
Then it all depends, I think that the 5D is an excellent camera, but there are very good reasons to prefer a D200 over a 5D, and landscape/wildlife are probably the 2 applications where the D200 has the most obvious value IMHO.