I would like to share this. At the Canada Post, the lady at the counter when I said 'need to send to Ottawa' she understood that I am sending passport for PR. The moment I got the envelopes, I took the pictures of both tracking number. I took the package back to her unsealed as she insisted. And before sealing she removed the return envelope's tracking number slip and gave it to me saying that I would need to track it.
One thing I forgot is to buy and stick "signature required" on the return package.
I will keep you posted..