I'm drving to Newfoundland next week for a moose/caribou hunt. Can anyone tell me if I have to declare my rifles, optics and cameraa at U.S. Customs before crossinmg the border?

Well, it's often a good idea so they are recorded and you aren't charged duty when you return.

The US form is CBP Form 4457, Dept of homeland security, CERTIFICATION OF REGISTRATION FOR PERSONAL EFFECTS TAKEN ABROAD