You can bring all your rifle parts, but not the body.
Gear is fine
Accesories are fine (but not your grenades for m72, or silencers)
Just put everything in your luggage, not your carry-on.
Once in Canada you can meet an age verifier, he can age verify you (18+) and then you can have a importer bring in a metal body for you from almost any supplier.
and many more.
P.S I miss the summers in Szczecin.