Both Canon 1D and Nikon D2Hs have 4.0 MP resolution sensors but Canon 1D's sensor is APS-H (28.7 x 19.1 mm ) and Nikon D2Hs's sensor is APS-C (23.7 x 15.5 mm ).
Since Canon 1D's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Nikon D2Hs.
Below you can see the 1D and D2Hs sensor size comparison.
As seen above, Canon 1D has a 1.5x Larger sensor area than Nikon D2Hs. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.