Canon 80D has a 24.0MP APS-C (22.5 x 15 mm ) sized CMOS sensor and features DIGIC 6 processor. On the other hand, Canon 1Ds MIII has a 21.0MP Full frame (36 x 24 mm ) sized CMOS sensor .
Below you can see the 80D and 1Ds MIII sensor size comparison.
As seen above, Canon 1Ds MIII has a 2.6x Larger sensor area than Canon 80D. 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.