I have shipped a silver coin to Great Britain. US Postal service, and fill out the customs declaration form. It was a gift… went right thru. I’m told the Canada border paperwork is different, but it should be able to be handled by the postal service. Within the US many companies use “Registered Mail” where each piece is tracked by every handler, and locked up in secure storage areas. Registered is for high-value fungible stuff like coins and jewelry, and probably doesn’t carry across the border. But I would think the postal service would be able to handle it… with the proper declarations.