In the absence of a more concrete answer I think (think!) this is a UPS-specific document that allows them to act on your behalf for the import process.
I remember dealing with this a long time ago and i'm pretty sure it also allows them to charge you their ridiculous fees.
If the tracking information shows the item is in a location that's not too far from you, you might still have time to short-circuit UPS and self-clear it. If you inform UPS of your intent then visit the CBSA office in the evening/night the clearance process takes minutes and the CBSA guys are awesome to deal with.
Check the CBSA web site (no link, sorry) for the classification of the item and that'll tell you the duty and tax liabilities, then just be ready to pay that when you arrive. You could also let the CBSA guy/gal do that onsite but they tend to appreciate it if you've done a little homework in advance.
Pretty sure you'll also need the "Commercial Invoice" from UPS so CBSA can stamp it. Then provide the stamped copy to UPS and you can either pick it up from them or arrange for local delivery (which you already paid them for).
This goes back a while so the process might not be exactly the same but it's likely to be similar.
Do that once and you'll remember to never, ever use UPS for cross-border shipments