Treasure of the Long Sault — Monica Hughes

In the early morning of November 11, 1813, the day of the battle of Crysler's farm, a young Canadian, Alexander MacAlpine, is found hiding in a ravine among enemy troops. MacAlpine is accused of giving away the British and Canadian positions to the Americans.

But he has an alibi: he's been out hunting for Indian treasure and found himself in American territory when the battle broke out. But no one believes his story - that is, not until 150 years later when two boys holidaying near the farm discover the Indian treasure...