If you mostly want to shoot landscapes, get the 5DII. It's excellent for that:
"Pigeon Point Twilight" Canon EF 50mm f1.4 at f9; EOS 5DII at ISO 3200, 1/100. Handheld.If you mostly want to photograph birds, 7D is a better choice:
"Waxwing and Winter Berries" Canon EF 300mm f4 I.S. at f4; EOS 7D at ISO 1600 and 1/640. Handheld.Or...
"Waxwing All-You-Can-Eat Luncheon" Canon EF 300mm f4 I.S. at f5.6; EOS 7D at ISO 3200 and 1/640. Handheld.Of course, you
can use a 5DII to photograph birds:
"Red-tailed Hawk Flyby" Canon EF 300mm f4 I.S. at f5.6; EOS 5DII at ISO 800 and 1/8000. Handheld.
Note: I wouldn't normally use 1/8000 for this shot, but I'd been shooting in the shade and didn't have time to lower the ISO etc. when this photo opp flew by.And you
can use a crop sensor camera for a scenic shot:
"Morro Bay Harbor" Canon EF 20mm f2.8 at f5.6, w/B+W Kaesemann C-Pol; EOS 50D at ISO 200 and 1/400. Handheld.In general, you'll just get more "keeper" bird shots with the 7D (or 1D MarkIII/IV, 50D, etc.) primarily thanks to better tracking of moving subjects... Or will find that the 5DII (or 1Ds MkIII) lends itself more to landscapes, mostly for the additional fine detail that allows for really big prints.