Permettez-moi de répondre en anglais afin que les autres intéressés puissent comprendre.
Claire's msg shows that children were being born from the two wives simultaneously. Difficult to justify if this is the same Francois Chabot.
Francois (son of J.B. Chabot and Geneviève Isabel) and Angelique were married on 25 Nov 1771, Montmagny.
Let me address your hypothesis:
a. You said Francois wed widow Boulet of Pierre Vallière. OK.
b. Then Francois becoming a widow of Angélique, he married Genevieve Gagnon. Wrong: Angélique died on 28 Jun 1799 at Baie-du-Febvre (Yamaska). So, she was still living when Francois Chabot had children with Genevieve Gagnon, although a proof of marriage has not been found. In fact, Angélique died after Francois. The latter died before 15 Apr 1790 (La Pocatière) because that is when Genevieve died as a widow of Francois. Given that Angelique Boulet who died in 1799 was the widow of Francois and the dauther of Guillaume BOulet and M.-A. Dandurant, there is not doubt that were are dealing with Francois' first wife. On the other hand, in her death record, Genevieve Gagnon is identified as Chabot widow and daughter of Jacques Gangon and Madeleine Pinel. In the absence of her marriage record to Francois, correlation with Genevieve and her parents cannot be correlated.
Let's keep searching.