imported post
If it is a handgun it's in the restricted category. There isonly two ways to transport a restricted firearm through Canada. One is two get a Authorization To Transport ahead of time. They usually only give these out for competitions if Canada is your destination. It's possible to get one for a transportation through Canada back into the U.S.A. like going to Alaska but it takes a lot of time and patience dealing with the bureaucracy. The other way is to get a firearms license in Canada the same as a Canadian who wants to buy a handgun.
Shotguns and Rifles that Canada doesn't consider an AssaultWeapon are non-restricted. Also except a M1 Garand or an Enfielda riflemust not have magazines larger than 5 rounds. Non-restricted firearms can be declared at the border, a form filled out and a fee paid.
I got this information from this website.
http://panda.com/canadaguns/#att
IMHO if you want totravel witha restricted firearm. Drive around lake Erie. Even if you do get a ATT you would need another one for your return trip and you can't take it out of the locked case and load it anyhow.
Another option is to ship it toa FFL at your destination.