For your portrayal of Cana- what exactly is your views on how her Cards Work? Like, is she capable of also using them like Tarot? Without the use of magic, or is magic her main use for them?
Obviously Cana’s main magic is card magic. She uses them to create different effects, and in my opinion it is an extremely versatile type of magic. Not only can she use it to create different types of elemental magic, she can blend multiple elements together. She is able to set traps, and even put people/things into her cards, which is kind of sub space magic. In general I just think her magic is awesome and honestly so underrated.
Now in terms of reading fortunes, I don’t necessarily think it needs magic like her card magic. I read tarot and head canon that it works the same in Earthland as it does here. In canon she started using the cards to predict when Gildarts would return, and from there she began to learn card magic. That to me suggests that one would not need to be a mage to use cards for divination.
With that said I think being a mage is something that can help boost her fortune telling abilities, and give her an edge over other non mages. Since it was actually her mother who left her the cards I personally headcanon that Cornelia was a fortune teller, and that the ability, or natural affinity was also passed down to Cana.
As for how she uses her cards I believe she uses them in multiple ways to make her jobs successful. She can take fortune telling jobs, where she would only need to use her skills in divination. But I think those skills also help her on more dangerous jobs. She would be able to use them to gain information about whatever she was up against, and then using her card magic as both offensive and defensive magic.