Those are different resource pools
Unlike grit, luck and panache, that clearly do have interactions between each other in the rules:
Grit, Luck, and Panache
Grit, luck, and panache represent three different means by which heroes can gain access to the same heroic pool, using it to accomplish fantastic feats. For characters with a mix of grit, luck, and panache, they pool the resources together into a combined pool. (Those who use panache and luck gain twice their Charisma bonus in their pool.) For feats, magic items, and other effects, a panache user can spend and gain luck points in place of grit or panache points, and vice versa.
Neither the Magus's Arcane Pool nor the Arcanist's Arcane Reservoir have anything that will let these pool interact, or allow you to share abilities from one class with the other.
There are, obviously, exceptions to this. Like the Blade Adept Arcanist Archetype, which uses the arcanist's pool to fuel her magus-like abilities.
A blade adept can select any of the following magus arcana, using her arcane reservoir in place of the magus’s arcane pool.
If you are thinking into multiclassing those two, you should really take a look into this archetype.