Why would you want to take a weapon into the U.S. when you can just stop about anywhere and buy one? If it's from a private citizen, no background check, even some pawn shops will sell to you w/o even asking for ID, though I think it's illegal. I have a friend who's a gun collector in Wyoming who buys stuff w/o ever having a background check.
You can buy about anything you want just in the want ads. Of course, I realize this would be more expensive than bringing in your own gun, but you can always sell it before going back to Canada. YMMV depending on the part of the country, but in places like Montana and Idaho it's easy to buy guns.
