There is a child buried in St. Antoine's Cemetery that is of the couple you mention.Here is what the church burial record states: Infant DUSSEAU, child of Jean Montmeny ad Marguerite Montmeny, buried 20 Nov 1821 in St. Antoine's Cemetery.
Do you have the genealogy for the parents of Jean Francois Toupin dit Dusault and his wife Marie Marguerite Montmeny?It can be found in the genealogical books "French Families of the Detroit River Region" by Fr. Denissen.You can purchase the books (two volumes) from the Detroit Society for Genealogical Research for about $30. They have a website. The Toupin dit Dusault lineage is on page 458-460.The Montmeny lineage is on page 851-853.If you have many French families, the book is worth the money.