Incomers often take over the pronunciation of a place. In NH, there is the Kancamagus Highway. The oldtimers say "kank a maw gus". The incomers and tourists insist on "kank a mang gus". That long A in Kancamagus that gives the "maw" syllable also appears in the Saco River, pronounced "saw ko". More and more, in recent years I'v heard "say ko".
OK, Mackinac Island MI pronounced Mackinaw.