Since this thread is a year old, I guess I will expand on my previous post.
I've talken over a dozen moose (14 to be exact) in parts of Canada, and although they tend not to be quite as large as their Alaskan cousins, any .30 cal should do the job with the right bullet and placement. All but two of mine were killed with a .300WM, the other two with a .270 and a .308. All but one was DRT. That one was a poor shot on my part and hit high. It required trailing and a coup de grace after 200 yards.
My favorite gun/load is a Pre-64 Winchester aforementioned in .300WM with the old Winchester 180gr "FailSafe" bullet. That's a Moose Knocker if there ever was...
Moose are not particularly hard to kill, although the vital zone is not much bigger than a large deer due to the size of the front shoulder. The ribs are as big around as a man's wrist, and the shoulder blade is stout. You want a big heavy bullet moving at good velocity. (.30 cal and up, 180grs and up, 2400fps and up) The .35 Whelen, .308, .30-06, .300, .338 all fill the bill. The higher powered .45-70 loads will do fine, and the 405gr Buffalo Bore load suggested above will wallop the biggest Bullwinkle on the planet.
Going back to your original post, as someone who has worked/hunted/lived/trapped/guided in the Northern bush, Canada not Alaska, you'll find a 12ga and a .22lr much more useful than the big bore. I spent 8 weeks on a winter trapline once with a 12ga, .22lr, and a .300WM. The .22lr saw daily use, but I can never remember taking the .300WM out of the case except to oil.
If you're serious about killing a moose, invest in a good pack board, chainsaw, 3 1/2lb axe, and a block-n-tackle. A gamesled is also helpful. Moose never die where it's "easy" and it is usually in the water/bog/swamp or in a gully/wash-out. Plan on packing 700+ pounds of meat for 3 or more miles. (That would be 14 trips on average, there and back, or 42 miles while packing a 60-70lb pack, 10lb rifle, in hip boots.........in the rain.....and the cold........with the windchill......)
Plenty of guys on here will spout nonsense about why one gun/caliber/mfg/ammo/bullet/etc is better than the next, and some are no-doubt knowledgable on the subject, but few can tell you from first hand experience how much hard darn work killing, cleaning, butchering, and packing a moose is.
Good luck and good shoot'n
t2e