Neither are particularly a good fit for the Beastmaster. I don't think that trying to shoehorn too many Jobs onto existing classes is a good idea. Remember, a Job only adds a limited number of things:
1) Stat adjustments
2) Five new actions and no traits
3) Different armor and a different subset of the main weapon type
4) Some tweaks to existing mechanics for the class
A FF XIV Job isn't comparable to something like a FFXI Job in of itself. It is more akin to a new selection of WoW talents within a class. The difference between a Summoner and Scholar in FF XIV has some similarities to a FF XI Summoner using different sub-jobs. The differences between a Dragoon/Warrior and a Dragoon/White Mage from XI are comparable to the difference between two Jobs in FFXIV (plus some added equipment differences).
You most important character customization decision in FFXIV will always be class, not Job. For example, every Conjuror Job will have access to the full range of healing, revival, and status restoration that the Conjuror possesses. Every Gladiator Job will be built on the basic framework of a dedicated tanking class. Other Classes have a bit more flexibility. Lancer and Pugilist have the basic framework to allow for tanking Jobs to be added in addition to their the current DPS ones.
That's why a Marauder pet-using Job is highly unlikely. The basic Marauder doesn't have any support for pet abilities. You could add a very minor pet, but nothing as focused on pets like the Beastmaster should be. On the other hand, the Marauder has all of the basic tools to become a powerful melee/AoE DPS class with just a few additions, well within the realm of a Job.
On the other hand, Arcanist to Beastmaster wouldn't really add much to the game. It already has two good Jobs, and Beastmaster would be hard-pressed to differentiate itself from them. It would be much easier for Beastmaster to find its own identity using a different base class. With a new base class, Beastmaster could provide all kinds of new actions to players.