As I see it...
1DII Pros: You own lenses already/1.3 over 1.6 for wideangle, pro build-quality, water/dust-proofing, 100% viewfinder & extra-bright viewfinder, better low-light AF capability, better over 800 ISO capability, enormous battery life (over 2000 frames per charge), buffer size, frame rates if you need it, Pro-level control layout.
20D Pros: Lower cost for nearly identical image quality, lighter weight, more compact, built-in flash.
As for landscape, the 1DII is only slightly behind the 1Ds for detail rendering. Given it has the faster buffer and better color off the chip, I would probably opt for it over the 1Ds UNLESS landscape was all I ever planned on doing with it.
Cheers,
Jack