When I was at the National Archives, I looked for info on Marie-Angélique Blais, but did not find anything.Maybe there is an error in Violette Allaire's book.
I did find in the PRDH and in the list of marriages of Varennes the following data :
Francois Allaire (Francois & Marie Chabot) marriedon February 12, 1787 at Varennes, Francoise Brunel ( Francois & Judith Lavigne). Francois and Judith were married on 28-05-1770 at Varennes.
Is it possible, this is the person you are looking for? I don't know.I did not research long enough to know.
I did find also in PRDH that a Francois Brunel (Francois & Josèphe...) married on May 25, 1770 at Varennes, Marie-Angélique Lavigne.A daughter, named Marie-Françoise. was born at Varennes on February 4, 1771 and her parents are FRancois and Marie-Angélique Lavigne.
Maybe I am off-track, but it could be worthwhile to pursue this info.