Congrats to Nova Man for FTF
An essential element of the dyke farming system was the
"aboiteau", a sluice that allowed water to pass out from farmland
into the ocean. Containing a trap door, the aboiteau would prevent
sea water from coming back in.
This particular site has had an aboiteau for hundreds of years,
being one of the major creeks that empties into the Minas basin. To
find the correct coordinates, answer the following question: Is the
stream water on the "farm" side higher at low or high tide? If the
answer is "high tide", the cache is hidden at waypoint "AA", on the
ocean side. If the answer is "low tide", the cache is hidden at
waypoint "BB", on the farming side.
For more info see this YouTube Video or
visit the Grand Pré National Historic Site. The video probably
isn't needed to solve the puzzle.