The Hawai'Ian Islands were unified by Kamehameha, the Maori Kingitanga never extended beyond the northern half of the north island our TL. This was home to at least two-thirds of the pre contact Maori population however.
When the earliest European settlers began making treks inland by the early 1800s, they discovered that the Maori had already begun adjusting their economies to export food products, mainly flour, flax and potatoes, to the convict colonies in Australia! They had functional mills they had made from pictures in European books!
An earlier settlement of Australia, or a delayed European settlement of NZ, would likely lead to a Maori-only "musket war" which should see the emergence of a single unified Maori King/State, or at the very least authority extended across the north island (ta ika a Maui) and the top end of the south island, perhaps as far as Aoraki (south island being the precontact place called Aotearoa. It infuriates me when the two islands have Maori names, but the shorter flatter northern island is called "the land of the long white cloud").
Definitely plausible.
Sources: BETWEEN WORLDS Early Exchanges between Maori and Europeans 1773-1815; Anne Salmond.
Penguin History of New Zealand, Michael King.
Nga Waka O Nehera - The First Voyaging Canoes, Jeff Evans.
Tangata Whenua: A History. Aroha Harris, et al.