Service Canada Passport Services has indicated on their website that original supporting documents will sometimes be mailed back separately from your passport application. The reason may be because the original supporting documents were receive from a dedicated unit that does all the scan of the documents. Passport officers assess every applications through scanned imagery. 

Source: https://twitter.com/PassportCan/status/1547241989153996805?s=20&t=VlpzrPnlNYFX6GG-WVqMfQ