I'd echo what everyone else said. If you want top dollar, grade the key singles - and then sell them on eBay, FB, forums like this - or go through a consignor to make it easy (you give up some of the sales, but it's simpler).
There's some big card shops in AB (Wayne's in Edmonton comes to mind) that would be a good place to take some - and get an honest option of what you've got.
If you pieced out the best 30 cards from that 20 year era, graded them, and sold them - you'd probably still have an easy time moving the remainder as "near sets" either locally through FB, listing them on eBay, on forums, to a card shop, etc.
For example: I had a set of 79-80 OPC. Condition was good, but not great. It was missing the Gretzky.... had it in a binder, had a reprint Gretzky in there to fill the spot in the page. It was a few years ago, but I got around $200 for it (keep in mind there are no other real great cards in that set. The "top" cards after Gretzky would probably be Howe, Hull, the Oilers Team Logo, the other "new" team logos, and maybe the Semenko RC?)
If the cards are all in really sharp condition, you should be able to find interested buyers. Just depends on how much effort you want to put in. Locally is a million times easier, because then you don't have to ship bulk.... but you're also limiting the size of your market.