Well Barbara, it could be your lucky day!
I just found the death record for Pélagie Beauchemin.
She died on May 8th 1880, Verchères, at 71 years, wife of Pierre Messier.
The witnesses were: Charles Beauchemin and Pierre Beauregard.
So it could be possible that Pierre Messier did married Adèle Brien.
Good Luck!
Claire