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 70D has a 20.0MP APS-C (22.5 x 15 mm ) sized CMOS sensor and features Digic 5+ processor.
Below you can see the 80D and 70D sensor size comparison.
Canon 80D and Canon 70D have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Canon 70D has 20% larger pixel area (16.91µm2 vs 14.06µm2) compared to Canon 80D, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.