SellerCloud can use a shipping carrier's API to obtain available shipping rates from the carrier and display them in a Rates window when manually creating an order in SellerCloud.
For UPS and USPS you would need to generate Request/Response Access xml files for the action menu. Again, this is only necessary if you do not have the permanent credentials form the carrier.
UPS - Check the Address Validation radio button and Use Customer Integration Environment (CIE) URL.
Download the files and email them to the carriers.