You are in Canada.
Unless you are in Calgary, Vancouver or Toronto, where there are companies that will take your items across the border and ship them by USPS, or you carry the item across the border yourself, you will be using Canada Post.
Which will take the item across the border and pass it to USPS.
So.
Did you use Canada Post?
Did you take it across the border and use USPS?
Are you confusing USPS (the postal service) and UPS (a commercial courier)?
Did you print out the USPS label, stick it on your parcel and drop it in the mailbox? The postal system (and the Universal Postal Union) doesn't work that way?
Where does the tracking number tell you the item is now?
How long has it been in transit?