*NO* 20D has the EF-s mount, while the film camera has the EF mount.
That lens will mount find on both cameras, but the 20D has the EF-s mount, not the EF.
Now, a lens that mounts on the film camera will mount on the EF-s mount with absolutely no issues.
An EF-s lens will not mount though on an EF camera.
The sigma will mount just find on the 20D as that camera can take any lens whether it is EF or EF-s. (It will also mount fine on the full frame camera)