Metis does not have an accent in English. Plain English style does not encourage using foreign words, especially when an English word will suffice. Metis with no accent is not a foreign word, therefore no accent is required. It is an English word with Latin-Romanic origins. You can find that information in the Oxford Dictionary. French writers may use the word with an accent, but it is a word that has also been adopted by the French language. To use the accent in English writing is either an error or an affectation.
Although many people who have a part-French lineage consider themselves Metis people, there are also many who consider themselves Metis people and have no French origins. The word is supposed to have originated in Romanic language, and while it may have come to English first via French, it was brought into English without an accent. Indeed, the original Romanic MESTIZO did not seem to have an accent. Why then, would Metis be percieved to require an accent in modern-day English? English rarely uses accents of any kind, except to help with pronunciation of foreign words. English has adopted many Romanic words without adding accents.
This editor would like to encourage the author of the article on Metis people to amend the word Metis throughout and to remove the accent when Metis is used as an English word.