I wanted to mail my application via Xpressport but unfortunately Canadapost (inside SDM) was closed by the time I reached (around 7 PM, Sat, July 3rd). I didn't even have letter size envelope as I was planning to use the Xpresspost envelope itself. So I just picked small passport application envelope available next to Canadapost counter, inserted my application in it after tri-folding (including citizenship certificate), bought the stamp from SDM and mailed it right away.
I took two risks that day
(a) Regular mail instead of Xpresspost
(b) Tri-folded Original certificate
I called Passport Canada over the last couple of days and finally they were able to find my file information in their system yesterday. Here's my timeline:
July 3rd: Application Sent via regular mail (from Toronto)
July 7th-9th: Application Received (Estimate no tracking)
July 20th: Applicated Opened/added in the system
CC is not charged yet, I will update the physical condition of my certificate and passport once I receive it (hopefully in a few weeks).