I took my 18-1/2"-barrel shotgun along on my driving tour of Alaska, Yukon, and NWT last summer. The page at
http://www.rcmp-grc.gc.ca/cfp-pcaf/fs-fd/visit-visite-eng.htm provides your options and will help you decide whether you can take the specific guns you want to take. I went the Option 1 route (Non Resident Firearms Declaration). I hit two problems:
1. At Dawson Creek, the gun shop at Mile 0 of the Alaska Highway at first refused to sell me ammo. They said the NonResident Firearms Declaration did not permit me to buy ammo- only a PAL allows that. Fortunately, I had printed off the web page and it says it IS good for ammo purchase (under 'Buying or Importing Ammunition'). Once they saw that, they sold me the ammo and apologized for the mistake.
2. The form is good for 60 days and is supposed to be easily extendable by calling an 800 number. By the time I re-entered Canada on my way home, I had less than a week left. I attempted to get it extended but was never able to get through the bureaucracy to get it done. I made multiple attempts but was never able to talk to a person, it was always an answering machine. I left messages to call my cell, to reply by email, etc, but never received a response of any kind. I decided I had no choice but to cross the border again (I could make it to the border at Stewart BC/Hyder AK before the expiration date) and pay for another permit even though I'd only need it for a few days until I got out of Canada. However, when I explained my problem to the border agent there, she extended the date on the old one (at no additional cost).
Also- if you happen to be taking an auto shotgun, note that the capacity limit is five. And plugging a larger-capacity gun to five doesn't qualify (according to the person I talked to at the Canada Firearms Centre).
Oh yeah-- the cost for the Non Resident Declaration to be processed was $25 last year and that appears to be the case again this year. That's a flat fee for all the guns on the form.