Norm..I am a Hay River Local and thought I'd help by illustrating your post.
The MacKenzie is big water..like travelling on a lake with current when it gets windy.
The Hay River is fairly Placid near town
The Great Slave is a big Lake
Beaver Lake is big water at the beginning of your trip..a great campsite on Brabant Island just before Baver Lake other wise pretty grim.
Providence is a nice stop...9.5 knot current on the way in!
You can often see bears swimming the river after Mills Lake... By the way Mills lake is very shallow can really blow up in a stormand offers nothing for camping spots.
Camp-Sites on the river are often a bit cramped in high water..a small tent might help (ours is of course huge).
Jean Marie River, in a wind
That's as far as we got this summer.