Recycling metal cans is ok as long as the metal is aluminium. If we are talking steel, there is no easy way to crush them flat for efficient storage and transport: short of giving them a good sledgehammering
To make life easier, simply disrupt the part of the design that provides such structural strength: their seams.
Each can would be opened at one end in the usual way and the contents removed. I’d imagine using an electric, wall mounted opener in which the can was free to rotate about a diameter halfway along its height (using eg a big suction cup, to help pour the contents into a bowl). A wide variety of can sizes could be dealt with by this technique.
This would allow the opener swiftly to deal with removing the other end of the can. The remaining open-ended tube would be much more easily flattened by use of a smallish lever (in the same way as Al cans are now).