Start here
http://www.rcmp-grc.gc.ca/cfp-pcaf/form ... 09-eng.htmIf you are carrying a restricted firearm like I did(480 super redhawk) then you need to get it preapproved before you show up at the border.
"g) - h) If you are declaring a restricted firearm, please print the number of
your Authorization to Transport (ATT) and its expiration date. To find out how
to apply for an ATT, call the Canada Firearms Centre at 1 800 731-4000 in
Canada and the USA, (506) 624-5380 outside Canada and the USA, or visit
our web site at:
http://www.cfc-cafc.gc.ca before you come to Canada."
It looks like a lot of work but it was fairly painless. Just be sure to have your stuff together before you show up at the border. Once I got back to the USA on the Ak side all they cared about was the paperwork for my horses.