For me, Arcana, as the domain of pure magic, would be associated with the Music of the Ainur, the original "spell" the effect of which was to create the World, and the Valar associated with that domain would be those who had the chiefest parts in the Music and are described as strong singers or as receiving the most musical instruction and having the most knowledge of music. Magic is also described in Tolkien's works in terms of craft and making. The list would comprise many of the most powerful of the Valar: Manwë, Varda, Ulmo, Yavanna, Aulë, Nienna, and Melkor. I might also include Vána, the younger sister of Yavanna, "at whose song the flowers arise and open", who is described as singing a song of spring that helped bring forth the golden tree Laurelin.