Mackinac Trail, or Mackinaw Trail is the name for two related, but separate, roadways in the US state of Michigan.In the Upper Peninsula: US 2, previous designation of H-63, before the construction of the I-75 freeway H-63, the entire road between St. Ignace and Sault Ste. Marie In the Lower Peninsula: US 31, between Petoskey and I-75 south of Mackinaw City Old US 131, between Reed City and Petoskey.