6N as stated, very easy. I've never had any issue at all crossing at either Watertown or Ogdensburg here in E. Ontario, WRT to being questioned about having a hunting license or invitation. A good backup might be to email the SC venue you wish to shoot at and ask for confirmation the club will be open on day xx and that non-members can shoot. If you have an e-mail response to that on your phone, that might help.
If you were attending an NSCA registered shoot, you could show your registration at the border (again, only needed if questioned).
Lots of great sporting clays clubs in the US, and they're easy to get to with just a little prep. Enjoy!