http://www.5esrd.com/gamemastering/monsters-foes Is probably the first place to start with a Viking themed bestiary. Indeed, the whole thing is probably useful.
Edit: probably would be best to pick a few targets that feel fairly unique to the space. A zealot, for instance, is not that unique. It's a human. Draugr, however, are pretty specially Norse.
So, here's the start of a list
Draugr
Black skeleton (specifically spell casting ones and ice themed ones)
Skui
Effigy (though very close to golems)
Kraken (there is one in D&D but it's a Norse thing)
Gargangjolp
Hrokkvir (though very ent)
Borghild
Wight sovereign
There are probably some subsections of the boards and builds that would work well on this. D&D monsters as a whole tend to not be as generic/themeable as FOTN ones. Yes, occasionally you get a theme add on (flaming lizard men, ice bats, etc) but generally a kobold is a kobold is a kobold.
Making builds of classes would probably help too.