What country in Oceania, with Matu-Utu (on Ile Uvea) as its capital, uses the franc as its currency?

The Oceania territory with its capital at Matu-Utu and the franc as its currency is Wallis and Futuna.

Wallis and Futuna is a French overseas collectivity in the South Pacific, made up mainly of the Wallis Islands and the Hoorn Islands, which include Futuna and Alofi. Its capital, usually spelled Mata Utu or Mata-Utu, lies on Uvea, also called Wallis Island. The territory’s currency is the CFP franc, with the ISO code XPF, which is commonly called simply the franc in everyday use.

The territory has an unusual constitutional arrangement. France handles many governmental functions, while three traditional kingdoms—Uvea, Sigave, and Alo—retain customary authority. Wallis and Futuna became a French overseas collectivity in 2003; before that, it was an overseas territory.

It is easy to confuse this answer with New Caledonia or French Polynesia, which also use the CFP franc. However, the combination of Mata Utu, Uvea, and the South Pacific territory’s two island groups uniquely identifies Wallis and Futuna.