Hi Akki045,
Congratulations!!
I am in a similar boat as yourself (Indian residing in US). It seems many people do send their passports out of the country. Sharing my experience below:
I personally used FedEx. In brief: I created an online fedex account ( a personal account), and using the FedEx Ship Manager (not the Ship Manager Lite), created a shipment which included a return label. I also opted for the commercial invoice to be generated for both onward and return packages as I had heard that some people (who had sent their passports to Ottawa from US) had reported that they were asked by CIC to provide a new shipping label with a commercial invoice.
You can use the passport processing tracker on myimmitracker here:
https://myimmitracker.com/en/ca/trackers/passport-processing-tracker
to get an idea of the kind of wait times experienced by ppl.
TLDR:
The shipping labels created with selecting a package type of an envelope, along with a document type of immigration papers declared at value of $1 for both onward and return packages. I had purchased one large bubble-wrap envelop (which could take 11" x 17" sized docs) for the onward package and a medium bubble wrap envelope (which could take a 11" x 8.5" doc). For the package type, I measured the bubble wraps envelopes that I had and put those dimensions in as custom. I collected all docs (pport, photos, annex a, return envelop), took everything together and wrote a simple cover letter explaining the documents and artefacts included.
The Fedex shipment gave me quite a few documents printed out.
4 labels for the onward shipment, 2 commercial invoices for the onward shipment. I made sure everything on the onward label was correct, and signed the two commercial invoices and included them in the standard fedex ziploc pouches that affix on top of the envelope (they just give you a couple of those at the fedex locations if you ask for them).
I affixed a similar ziploc pouch on the return envelope. I put the 3 return labels within the pouch.
I took:
Coverletter
The passports
Photographs
annex A
fedex return shipment instructions
fedex return commercial invoice (separate from the labels that were put into the return envelope's pouch since they had to be signed by the person returning)
return envelope with return labels within the pouch,
and put all of the above on the onward and sent the package. The cover letter that I wrote , explained exactly what each thing was.
Hope that helped even though am a bit late.