User blog comment:IamJakuhoRaikoben/Sorcerer Magazine, Issue 42: June 2015/@comment-25395791-20150704034940

Nowadays, it is discussed whether Juvia or Cana is a stronger Fairy Tail Mage. Both of them have their strengths and weaknesses, something which will be covered here. On the one hand, Juvia is stronger due to the good potential she has as well as her astonishing power. With her body being made of water in the first place, enemy's attacks, most specifically projectiles, do not have an effect on her, rendering most of Cana's attacks useless. Furthermore, despite her already outstanding Magic Power, Juvia can get even more stronger if Gray is in her presence or is even mentioned in a conversation. For example, while Erza and Juvia could not defeat Meredy together, in the end, Juvia managed to defeat the former by herself easily, just with Meredy stating her intention of killing Gray. Being strong and deadly at times, Juvia indubitably holds a title for one of the strongest female Mages of Fairy Tail, even leading many people to believe that she is actually the third strongest female Mage. On the other hand, Cana shouldn't be underlooked as she definitely has a potential to be one of the strongest. For instance, despite her initial failing to cast Fairy Glitter on Bluenote properly, Cana was able to finally succeed during Grand Magic Games. However, her defeat to Bluenote should not be taken seriously in this case, as neither Juvia would most likely not be able to defeat the latter as well, with him belonging to the same category as Gildarts and thus ultimately making the two female Mages somehow even. Nevertheless, even without Fairy Glitter, Cana's Card Magic is powerful and versatile enough by itself as she has a wide range of spells to choose from against Juvia, such as lightning attacks or even trapping her target inside of a card dimension, making them helpless. Therefore, Cana should definitely be taken seriously as even Hiro Mashima, the creator of the series, himself stated that she holds the third or fourth place for the place of the strongest female Mage of Fairy Tail. In conclusion, both Cana and Juvia are very powerful and have a very good potential with their Magic. However, if I would have to choose between the two, I would rather go with Juvia as Cana's strength hasn't been pointed out so well as Juvia's has been in my opinion. Nevertheless, this does not mean she is weaker but rather just not given enough spotlight for me to make a proper judgement of her skills.