US to Canada, US to Mexico, Canada to US or Mexico to US.
Each country has Border Agents/Customs for reasons.
Follow the RULES
Rules for Bringing a Firearm into the U.S.
If you want to visit the United States with guns or ammunition, you will need a permit from the ATF. This applies even if you are a diplomat, foreign law enforcement agent, or hunter.
As of 2014, you will need to fill out ATF Form 6NIA to receive a permit. This is also called ATF Form 5330.3D Application/Permit for Temporary Importation of Firearms and Ammunition by Nonimmigrant Aliens. Processing time to receive approval varies, but can easily be as long as 2 – 3 months. The permit is valid for one year. You may use it to cross the border with your firearms any number of times during that period.
The form must include serial numbers of all firearms and any ammunition you will be bringing into the country. You will undergo an ATF background check. If you have a criminal record it may very well affect your ability to get approval. Your form will be returned to you indicating whether or not it has been approved.
When you arrive at the border, you will declare your firearm, provide the required documents, and answer all questions truthfully. The border services officer must be satisfied that you have a valid reason for importing the firearm, and may check to ensure that you have stored your firearm properly for transportation. They will review your paperwork and may verify that the firearm you have with you matches the one described in the documents.
