In theory both logic and charisma should be applicable to choose as a drain stat in regards to norse magic. The ancient norse had several types of magic one being Galdr which is the one focused on memorization, chants and incantations, so in essence fairly hermetic in its practice, the other being Seidr which was more akin to a shamanic tradition and was mainly practiced by women, while male prationers of Seidr did exist it was considered an unmanly practice, though Odin,the chief male God of the norse pantheon practised it on numerous occasions.
So depending on whether you want your norse magician to be a practioner of Galdr or Seidr, you could choose whether you wanted to use logic or charisma, just to have a little more flair and actual realism to the tradition.