Looking at varangur since i can get two armies for the price of one just about (swap as northern alliance maybe) but some of the units im not sure about.
I take it sons of korgann are maybe heavy horsemen yes? Big bulky armor etc?
Kruufnir??
I get an idea of draugr from some other posts on here.
Reavers im unclear on.
Mounted Sons are indeed heavy cavalry. Anything in heavy armor on a horse should do fine.
Kruufnir is a snow troll, basically just an upgrade to the Snow Troll Prime.
Reavers are berserkers on foot, lightly armored, probably big weapons.
Thank you very much
Pretty much covered by @Luke
Mounted sons are basically huscarls who have learnt what horses are!
Draugr are (fluff wise) zombie type efforts, but any cr*p looking infantry will do the job.
Reavers are archetype berserkers - forgot pants, but did bring a couple of axes.
Kruufnir is a monster hero, so build as you feel appreciate!