Having served 2 tours in Europe with NATO. I can tell you that CBSA is CBSA for everybody. There is no special treatment for military personnel.
This is how it went for me: I had to submit a complete inventory of everything my family and I owned. All of my belonging were loaded into a small container by civilian local movers. We had 5000 lbs worth of stuff and 47 pages of inventory. The custom officer looked at and stamped all 47 pages and the way we went. I have no idea if he looked inside the container.
After my first tour, I brought back a RS M1911a1. I had no problems with CBSA. The pistol was sent separately and was kept by police in Canada until I took the proper courses and got the proper papers. I had 6 months to do so.
So, the only thing that differs from the laws of imports here is that the airgun already belongs to you and that you've been in Europe for 2 yrs. Personally, I would show it on my inventory as a BB gun and shove it in the container.
Your media induced paranoia is interfering with my freedom.
Aging is a disease and everyone has it. A pandemic for which there is no vaccine. And, if you live long enough, it will kill you.