Agree with others no travel agent needed.
To get into Canada, you need a form RCMP 5589. You can prefill it JUST DON'T SIGN OR DATE IT. When you get into Canada their customs agent will inspect the rifles and check that all serial numbers match the from, they will then have you sign the form in front of them and pay $25.
To get back into the US, prior to leaving you can get a 4457 form filled out, I have never been asked for it though. I guess it depends on where you live as to if they want to see it. I will say it doesn't hurt to have it just in case.