Karlsson and Cowen are not going to make a good pairing IMO. Cowen isn't suited to play at the high tempo Karlsson does, so he just gets left behind. You pretty much have to use all 5 skaters in every zone now, so it's just not going to work.
I think Methot is the best bet to play well with Karlsson. He's average at just about everything and has no major deficiencies, so he won't really raise the play of his partner but he won't slow down a better one either.
Wier and Ceci both play at a similar pace and both can move the puck well, so they complement each other nicely. Pair them up so they can pass the puck to each other to deal with heavy forechecks. They also played well together for the last 5-10 games of last season.
The last pairing is going to be the one that loses them a bunch of games. Gryba is the best out of the 4, so put him on the right side, rotate the other 3 through the left side and play the best performer for most of the games. Try really hard to keep them off the ice against anyone other than 4th lines and weak 3rd lines. Have them focus heavily on the PK.