I had the same question, so I emailed them. Here is the response:
"Dear Applicant,
You may request your documents to be shipped to your residence or other address in Canada at an additional cost of $26.00 CAD, or select a BLS location or another Canada Post office at an additional cost of $24.00 CAD.
For a list of authorized post offices, please go here: https://ais.usvisa-info.com/en-CA/niv/information/courier_dropboxes
Go to https://ais.usvisa-info.com/en-ca
Click on Sign in to log in to your account.
Click on the option Continue, then on the link Request Premium Delivery.
Make the selection:
Pick-up at a courier store location: 24.00 CAD
or Deliver to a personal or business address: 26.00 CAD
Follow the instructions and enter your delivery address or choose your courier pickup location and complete the payment.
Sincerely,
The Contact Desk Support Team."