@84FLH I have similar plans as you, except that I'm not quite retirement age yet. I ended up going with a small "off road" trailer for several reasons. One, if you're planning to set up camp in one spot for a while, you can leave your camp set up while you drive your truck to different trailheads (or anywhere else) and explore. You have less indoor space, but actually more living space in total once you set up awnings and the outdoor enclosure room. Plus I have my entire truck to carry gear. Unless you get a really large camper, I don't know how people have the space to carry their stuff when doing long trips (I'm thinking something like a FWC - there is hardly any storage space).
The second is that I bought an F150 (1/2 ton truck) assuming it would be fine to carry a slide in camper and after I owned it realized I'd be over GVWR with anything more than a shell-type camper (especially since I have the 5.5' bed). So if you do want a truck camper, definitely get a 3/4 ton or 1 ton (250/2500 or 350/3500).
The trailer I have is small and maneuverable. It's composite with an aluminum exoskeleton and it's very well built. It would probably outlast my truck on extended rough roads. You do have to be careful about going way down a very narrow road and getting into a pickle if you need to turn around and cannot. Although that can happen with a large truck/camper combo as well.
I'm going to add a 180 degree awning with walls to the other side. So I have a ton of living space if needed in extended bad weather. Although I have to admit, it would be nice sometimes to be completely "indoors" when making dinner or making coffee when it's really nasty outside. On the other hand, this forces me to be outdoors which is the whole point. If I was planning to live in this setup for the rest of my live (as opposed to 6 months or a year) I think a van would be the better way to go (or truck/camper).
If you're planning to move from place to place every day, then this is far from an ideal setup. A van or truck camper would be better. But if you want to set up somewhere for a week at a time and explore, then I think there is a lot to be said for a trailer. If I had to do it over again and money were no issue, maybe I would get an F250/350 and a slide in camper or maybe a sprinter van. We'll see.
With respect to guns and Canada, you can take something like a shotgun or rifle with you through Canada if you're on your way to Alaska and fill out the proper paperwork. You can also have a gun shop in Montana ship your firearms to Alaska and you can pick them up there.
Like you, I used to do a ton of backpacking (thru hiked the PCT in 2004). Now I like to have an enclosed place to sleep (especially in grizz country) with a comfortable mattress and do long day hikes instead. FYI, this summer I plan to do an extended trip through WY, MT, and ID. The summer after that, through BC and up to the Arctic circle. I would have no qualms about taking this setup on the Dalton or Dempster Hwy.