Copying the PO and re-submitting gives a new PO#, so from the supplier's perspective it is a different PO.
ByD in this is inconsistent - on some Business Documents (e.g. Delivery Notification) a cancellation can be undone, on others (like POs) this is not possible. We have also had issues where someone accidentally cancels a PO, at which point you have a nice little mess on your hands that is not easily fixed.
So: being able to undo the cancellation of a PO would be a good thing.
Regards,
Eelco