I am afraid that your item may be returned to you back.
I guess when you are sending any package or letters to P.O box you should not ask for "Confirmation of Delivery with signature"
because it is P.O box, no body will be there to pick your package and sign.
and now I doubt someone from CIC will go to post office and pick your package.
I also sent my package to P.O box but did not opted for delivery notice.
from Canada Post web site it shows that some one called Dave Turpin signed.
but CIC has not confirmed to me so far that they have my package...
this process is all a big mess....