I found three good options. You can use all three, if you want.
Magnemite: It's easy to find, has good special attack, and has lots of resistances. It learns thunder shock at level 5, and isn't weak to any of Araquanid's attacks. The Araquanid is holding a wacan berry, which may slow down the battle. Also, don't be temped to use spark instead of thunder shock, as Magnemite's physical attack sucks.
Hawlucha: It has exceptionally high physical attack and speed for a Pokemon found that early in the game, which lets it take advantage of Araquanid's relatively low physical defense. At level 16, it learns aerial ace. Aurora beam isn't very much of a problem because of Araquanid's low special attack.
Oricorio: It has exceptionally high special attack and speed for a Pokemon found that early in the game, and it's very adaptable because it can change type by sipping nectar. It learns air cutter at level 13. Aurora beam isn't very much of a problem because of Araquanid's low special attack.
