Depends on what you're looking for, as they are really completely different kinds of fishing.
Canada would primarily be walleye and northern pike, and a variety of ways to fish for them (casting, trolling, jigging, rigging, etc.). If volume is the desire or almost total peace and quiet are your thing, Canada is probably the choice. We used to go to a lake in Northern Manitoba where you may not fish near another boat the entire week.
Personally at this point I'd choose Alaska. Primarily salmon, halibut, rockfish, etc. and each has one pretty specific method of fishing for them. That said, if your Dad is 81, aggressively jigging a very large bait or hauling in a large salmon/halibut might be a bit more physically taxing than he'd like.
Both phenomenal places, just depending on what excites you.