To unlock the Coureur des Bois trophy in Assassin's Creed III Remastered, you will need to sell undamaged pelts in all nine of the General stores available in the game. There are three stores in each of the game's three regions: The Frontier, Boston and New York.
To obtain an undamaged pelt, you will need to kill animals using your hidden blade.
You can find the locations below (credit to King fiShiZ on TrueAchievements for the screenshots.:
The Frontier General Store Locations:New York General Store Locations:Boston General Store Locations: