We've done the trip three times, the best one was the Cassier though the road was way worse and slower. Contrary to what was said above, you can take guns through, even a handgun. Please go read through the Canadian Firearms Center before listening to anyone on the internet. Even me. Might have changed some rules since I went through. I requested permission to take my Glock 20 through with me when I went down to Montana in 2008. The only issue I have is my little plastic case didn't make the border folks happy, they could pry the lid up and touch the gun, even though they couldn't drag it out. So I dug around in my stuff and found another padlock and with my knife scraped the handles enough to fit it on there to satisfy them. Here's the real interesting thing, the Canadians are more gun friendly than the US border folks are. They, at least in Alberta, Yukon and BC are much like Alaska and say Wisconsin and all hunters. That trip I actually got permission to bring my AR-15 through with me..BUT the guy called me from the Firearms Center and recommended I ship the AR down and not bring it through. He told me even though I had written permission, the border guards sometimes did their own thing and confiscated things and caused folks a lot of trouble and money, permission slip be dammed. So I shipped the AR. So with any guns you are planning to take through, they say you must have the gun in a locked case completely inaccessible to the vehicle occupants. They don't really recognize any sort of need for self defense particularly from 2 legged predators. They actually told me this so this isn't some "yeah my buddy said" BS, This is what really happened with my situation. I would honestly have to say I had more to fear from bears or moose than any 2 legged things up there...but with what is going on with terrorists now, I might think an 870 might be a good idea...placed strategically.. not in the truck but the camper closet or somewhere..
Saying all this, please go read the CFC...oh back then you could have so many KG of powder, primers, 5000 rounds of ammo, etc... the CFC I think links over to their explosives site which clearly gives these allowed amounts. I busted the powder amounts by double and the ammo by more than that but had it placed all through my household stuff and since I was on Military orders all the trips they were nice to me. They didn't even think I was some kind of criminal for having a gun with me. The American side though....even in Sweetgrass acted like you're a criminal and 20 questions, etc..
Oh, the milepost mag isn't mandatory but it is awfully handy..
There is a huge, long lake up in BC with absolutely stellar rainbow fishing. Rented a little aluminum boat for hardly nothing and fished it for three days. As others said above, it is still an epic road trip and should be done slowly as possible to enjoy it.