a.- If an order is imported in to GroovePacker and then cancelled (either before or after it is scanned in GroovePacker), how should it be handled? 

In this case you can search for the order in GroovePacker, select it by clicking it's row in the orders list, then choose "Cancel" from the status dropdown. This will mark it cancelled in GroovePacker. Inventory will be un-allocated and placed back in available.

b.- If a previously scanned and shipped order needs to be re-shipped for some reason how should it be handled in GroovePacker?

The best practice for this is usually to create a new order in the order manager with a suffix appended to the original order number. So if the original order is 1234, then the re-shipment would be: 1234-RE  

(or similar). The new order will import into GroovePacker like any other. This will properly handle inventory and make it easy to find both shipments when the order number is searched.