The farther out the lens sits, the more far focus range you lose with a simple ring adapter that has no glass elements. Which means the lens mount itself can be too wide to actually fit inside the mount and has to sit completely on top of the adapter. The diameter of the Minolta AF/Sony A-mount is smaller than that of Canon EF.

The throat diameter for A-mount is 49.7 mm. It's the mount throat diameter difference that causes the problem. You could build a fixed stop into the adapter to always hold the lens at, say, f/8 I suppose, but it would still be quite limited, even at best. Given the small difference in flange distances, neither of those would probably be simple or straightforward - but without it, you'd have no aperture control, so you could only shoot at the lens' minimum aperture (typically f/22) - pretty useless. In theory, an adapter with some sort of built-in servo could receive the electrical signals from the body and translate them to mechanical movement for the lens.

If it was purely mechanical, you could do stop-down metering. Since (most) A mount lenses don't have aperture rings, you'd have to build an aperture control into the adapter. Second, EF mount uses an electronic connection for both aperture and focus, where A mount uses a mechanical linkage for aperture, and either mechanical or electrical for focus (but electrical was introduced relatively recently, so most older lenses being adapted would probably be mechanical).

From what I recall of the diameters, they're similar enough that this would be extremely difficult, if possible at all (and I'm leaning toward 'probably not possible'). With a mount that's a lot smaller in diameter most of the adapter could sit inside the EF mount ring, and you could probably do it.

Minolta a mount lenses