It's coming sooner or later as an HBO series, so...
Shadow: Jason Momoa
He's big, strong, definitely has that "don't fuck with me" face, he can be dangerous but also very nice, and I would love him to play a complicated role where he isn't a barbarian. And Shadow MUST be a POC!
Wednesday - now this is hard. My absolute ideal Wednesday would have been Donald McIntyre in his prime:
But he is now old and he's an opera singer to begin with, so... I saw people suggesting Brian Cox, he definitely has the look.
Mr. Nancy: Morgan Freeman would be ideal, but he's too big a star for a tv series... :( But this is a dreamcast!
Loki/Mr. World: I have no idea. All the book says is that he has red hair, very short. I have seen Loki with so many different appearences that I have no actual actor in mind. Any ideas?
If only Andrew Scott was a redhead...
Laura: Jennifer Westfeldt
Never seen her play, based on looks alone.
Chernobog: Ernest Borgnine
He's 90-soemthing but still active and healthy and looks strong enough to wield a big hammer. And he's a legend.
Mad Sweeney: Steve Buscemi
He's an amazing character actor, although he probably isn't Irish... but he would be awesome in this role.
Hinzelmann: Ian Holm
Thing is, Hinzelmann must appear a nice, huggable old guy at first, one whom you would never suspect. Holm has this aura, everybody would be like "D'awww, Bilbo! Sure he is a super nice guy!", but he can be creepy as fuck if he wants (watch From Hell. Just watch it.) Or, if he's too expensive for a series, how about Ian McElhinney? Nobody would suspect honourable Ser Barristan to be a serial killer! (And he CAN be mean: he was one evil motherfucker in Hornblower.)
Mr. Town: Clark Gregg
The agents serving Mr. World look like your typical S.H.I.E.L.D member, and he would rock this role.
Samantha Black Crow: no idea. I don't know any young native American actresses, and she's another character who just can't be white.
Chad Mulligan: Liam Cunningham
Irish? Check. Honourable everyman look? Check.
The Tech Boy: John Bradley
He definitely has the look and he can still pass for late teens. After nice Samwell, it would be a good change to play a mean little dickhead.
Too many GoT cast members, you say? :D