I have Marie Montminy's death record and it says she was the widowof Jean-Baptiste so I would guess that that is her husband's burial record even though it says Jean-Baptiste.
Burial Record: St. Mary Catholic Church, Monroe, MI Maria Mominy In the Year of our Lord 1872, on the 11th of December, the burial of Maria Mominy, widow of Jean Baptiste Dusseau. Born on 4 February 1803. Died on 9 December 1872. Sacraments given.
I do not have Jean-Francois Dusault's probate papers, but I was told by someone who does, that from those papers, he died in Jan. 1855 but his widow did not probate the estate until 1859 because she was afraid it would cost too much.
Are you sure the burial record for Jean-Francois reads Jun 1855 and not Jan.?