According to the tour guide at Champlain's current church, steady river erosion has meant that the graveyard where Hilaire and Antoinette were buried, along with the adjoining land Champlain's second church was located on, is now underneath the Saint Lawrence river. This makes sense, as steady river erosion was apparently the entire reason Champlain's second church was abandoned.
Additionally, according to the pastor of Champlain's current church, the grave markers in Hilaire's time were made of untreated wood which didn't survive long enough to be moved when Champlain transitioned from its second church to its third, and furthermore the remains from Hilaire's time were decomposed to the point where they likewise wouldn't have been moved.
In other words, this photograph is probably as close as any living Brunelle will ever get to something akin to a grave marker for the first two Brunelles.
Personally, I like the fact that it contains both an anchor and the Quebec flag.