If you try to claim insurance and they deem it a firearm (I think even pellet guns so above 407fps and YOU have to prove its under 407 after its lost or broken) they will refuse the insurance claim. Canada Post will only ship guns Priority Courier, anything else and you are breaking their rules and they can refuse service. Also they x-ray packages before they go on flights if you send it airmail (priority courier and sometimes xpress are sent by air across the country) and if it happens to be a Purolator plane, they will refuse it if it looks like a firearm. Purolator will not ship anything even like a firearm and since they are owned by Canada Post sometimes packages are piggy backed.
Problems are rare and CP has zero right to know whats in the package unless its crossing a border, x-ray scans excluded. I have shipped dozens of guns over the past couple years and have never had a problem, always with xpress post, but I have never had to make an insurance claim.