I've purchased used scopes privately from the U.S. without any issues. Some even had words to the effect "used riflescope" marked clearly on the package and/or accompanying USPS paperwork. I do not make any cross border purchases from sellers who will ship only via UPS. The only exceptions are some of the bigger corporations who have negotiated flat brokerage fees with UPS. As far as I know, there is still a class action law suit against UPS, based on its outrageous and arbitrary fees, inching its way through the court system here.
Many scopes do come across the border successfully(unchecked).Nevertheless US law requires an export permit(on new scopes).Whether this policy is in effect with used scopes I do not know.As I said there is no dealer I am aware of who will ship new scopes to Canada and that includes Rick,Cabela's,Cameraland and all the others I have tried.I know of 2 Canadian citizens that were checked at border crossing by US Customs before entering Canada and had their scopes(purchased legally in the US)seized because of lack of export permit.They spent several uncomfortable hours talking to US Customs and Homeland security before they were allowed to proceed.Dept of State controls export of firearms parts and scopes.You could check with them. Monashee