Tonga has already been suggested, and I think that's a good idea. They had a fairly large empire at the game's start date, although it was crumbling against revolts in Samoa and Fiji.
Oceania in general needs more stuff. Maybe even a DLC/expansion of its own. It's probably the most boring region in the game right now, and not just in unmodded EU4; I've yet to see a mod that adds anything much in the way of content down there. Which is a pity, because there's a lot going on down there at this time. Apart from Tu'i Tonga, Tahiti may have been running a maritime empire in the Tuamotu Archipelago, New Zealand was still in the process of being settled by the Maori, and Samoa and Fiji had become independent polities alternating between marriage alliances and warfare between each other and their former masters in Tonga; their style of diplomacy would probably have been quite recognisable to Europeans at the time.
Oceania in general needs more stuff. Maybe even a DLC/expansion of its own. It's probably the most boring region in the game right now, and not just in unmodded EU4; I've yet to see a mod that adds anything much in the way of content down there. Which is a pity, because there's a lot going on down there at this time. Apart from Tu'i Tonga, Tahiti may have been running a maritime empire in the Tuamotu Archipelago, New Zealand was still in the process of being settled by the Maori, and Samoa and Fiji had become independent polities alternating between marriage alliances and warfare between each other and their former masters in Tonga; their style of diplomacy would probably have been quite recognisable to Europeans at the time.