When you say you included a pre-paid expedited USA shipping label, I am assuming it is not via Canada Post Xpresspost. From what I understood reading the passport request email sent by CPP Ottawa, they will only use the return shipping envelope if it is Xpresspost. If you sent pre-paid labels from any other courier company (DHL/UPS/Purolator etc.), they will not use those and instead mail the passport to you via regular postal mail. So chances are that it will be delivered to your friend's mailbox via normal post. I could be wrong, but since no one has posted anything so far, I thought of providing at least something to the best of my knowledge.
However, if the pre-paid Expedited USA shipping label is through Canada Post, it is still Canada Post but not Xpresspost. In that case, they will deliver it to your friend's mailbox as they do not require a signature on delivery. If they needed the signature, they would take the envelope back to their office and you would need to collect it from them. You can also have your friend collect the passport for you but he/she will need to have an authorization letter from you.
