the can is open
the can is empty
I don't know the atmospheric pressure or how to get that value
First you have to learn the words so you actually know what you are talking about. Force is not pressure. The difference depends on what you mean by "crush". If you mean to apply forces on opposite sides of the can, then the force will depend on the shape of the tool applying the force. (We would assume the force on the opposite side is just a wall that prevents the can from moving.) If you mean to pump air out of the can until the pressure differential flattens the can, then you have a very different experiment and you measure pressure, not force. You would do that by sealing a hose to the can and attaching your equipment to the hose.
You might mean to crush the can end to end. But that is not what air pressure does. So you must figure out what you are talking about.