You will not be allowed across the border without an approved BATF form 6N1A. You get it from their website, fill it out (simple) and then mail or preferably fax it in to them. It takes anywhere from 2 to 10 weeks to get it back, with 4-6 being average. You MUST include a copy of a valid US hunting licence. There are presently NO exceptions to this. It doesnt matter what the licence is for, it can be for any State for any type of game. It was alot different last year, but in the past year every border station has adopted a 'no exceptions' stance - you either have the approved form or you LEAVE your guns in Canada. For what its worth, once you're legally in the US, as long as you have a valid hunting licence, you can legally possess/purchase any firearm and ammo.