Let's say I were to only order packs CAN->US. Never from anywhere else. If I were to also send mail us->can would it be worth it at all to pretend to have a penpal/friend/family in Canada and that's why I get so much Canadian mail? Think your local post office would find it any more or less suspicious?
Try to remember you; like most of us, are just one person out of millions that get mail. Don't overthink things. If you were getting vitimins from Canada would you go to the trouble of a penpal? Just another peice of mail out of thousands delivered daily.
Just be smart, research your vendor and stay safe.