The marriage record for Parents Louis Mirau and Marie Richard seems to say they were from Acadia and detained as prisoners for 12 years during which time they had three children, a boy Frederic age 3 years 9 months and thirteen days, a girl named Elizabeth age 2 years 2 months and 10 days, and a girl Marie Esther age 4 months and 9 days without the benefit of marriage. They were married September 22, 1767 at L'Assumption, Quebec and the children legitimized the same day. This record can be found here -
"Québec, registres paroissiaux catholiques, 1621-1979," database with images, FamilySearch (https://familysearch.org/ark:/61903/3:1:3QS7-L99S-2XTH?cc=1321742&wc=9RLC-VZS%3A14637901%2C14637902%2C14637903 : 16 July 2014), L'Assomption > L'Assomption > image 178 of 588; nos paroisses de Église Catholique, Quebec (Catholic Church parishes, Quebec).
Other persons mentioned who may be related are Jean Richard, Francois Mirau and Jean Baptiste Mirau.
On the next page in the register are the baptism of the children of Pierre Mirau and also the baptism of the children of Francois Mirau. They can be found here-
"Québec, registres paroissiaux catholiques, 1621-1979," database with images, FamilySearch (https://familysearch.org/ark:/61903/3:1:3QSQ-G99S-2XPH?cc=1321742&wc=9RLC-VZS%3A14637901%2C14637902%2C14637903 : 16 July 2014), L'Assomption > L'Assomption > image 179 of 588; nos paroisses de Église Catholique, Quebec (Catholic Church parishes, Quebec).
On the page before is the marriage of Joseph Bourque and Marguerite Mirau ( a sister I presume) who have the same story about being prisoners and also have children who are legitimized by the marriage. This can be found here -
"Québec, registres paroissiaux catholiques, 1621-1979," database with images, FamilySearch (https://familysearch.org/ark:/61903/3:1:3QS7-899S-2XGP?cc=1321742&wc=9RLC-VZS%3A14637901%2C14637902%2C14637903 : 16 July 2014), L'Assomption > L'Assomption > image 177 of 588; nos paroisses de Église Catholique, Quebec (Catholic Church parishes, Quebec).
Bob