I just made the drive from Washington State through British Columbia and Yukon Territories, to Fairbanks, then back a couple of weeks later. So, two entries into Canada, with my rifle in my Jeep.
No problems.
But - I'd printed out and filled out the Canadian form referenced above ahead of time.
I also declared my rifle to U.S. Customs before leaving the U.S. They wanted to see the rifle and serial number. That made entry back into the USA with it a few weeks later easier - and interestingly the Canadian customs officers also liked seeing that I'd registered it with U.S. customs.
Canada took my credit card for the $25 entry fee, which was good for two months I believe, so it covered me on my crossing from Alaska back into Canada.
Also, everyone, U.S. and Canadian border officers, were happy that my rifle was locked in a hard case, with the bolt removed and the ammo stored separately. Not much good for bear defense that way, but very nice and safe for transport and the customs people were happy. If they're happy, I'm happy.
I'd taken rifles into Canada before, for shooting matches, but that was quite a while ago. It's not particularly tough to do. Just use the right forms, prepare things in advance, and I'd recommend declaring the rifle at U.S. Customs before leaving the USA, it made re-entry into the USA with the rifle very smooth. In fact the same border agent inspected my rifle on the way out as had on my way in a few weeks earlier.
BTW - I only had 40 rounds of ammo, and again, that seemed to please the good people at the border. I think they get a lot of folks who try to bring arsenals of weaponry and ammunition through. It's an international border, respect that, and all goes well.
Regards, Guy