Well the biggest problem would be size; it would be the largest nation on earth by some amount and not an area that one could effectively exercise control over- figure that French Polynesia alone is about the size of Europe (and not a place that France effectively administered outside of the most populous islands until well into the 20th century. So all of Polynesia would be of an order of magnitude much greater and would be very difficult without modern technology- especially surveillance or communication.

Even then, Polynesia doesn't have a history of being united- few archipelagos, much less Islands were united under singular political authorities. But the political authority- or the idea of a state- didn't really exist in the same way it did in Europe in the 18th century- so it can be hard to draw explicit parallels. Either way, there was no extensive unifying body though. Furthermore, many of the Polynesian states that exist today are proudly independent- Tonga, Samoa, Fiji (if you count it as Polynesian-ish)- and wouldn't necessarily be interested in losing what they see as their ancient sovereignty over their islands. Which can be an especially sticky subject when you consider the long history of colonialism in Polynesia- it was largely the first place targeted by French and British imperial ambition and was almost entirely carved up over the 19th century- and many of the islands (Aotearoa, French Polynesia, Hawaii, American Samoa are still held by settler populations or foreign metropolis)

The area of Polynesia is also not really that well defined; while the triangle formed by Aotearoa, Rapa Nui, and Hawaii makes sense, there are a lot of Polynesian Outliers- that is Islands that were settled by navigators who went West instead of East and exist in parts of what are otherwise considered Micronesia or Melanesia (take the Loyalty Islands for example).