Back again.I did not find the marriage of Jean and Marguerite in either Bathurst, Petit-Rocher, nor Robertville, but did manage to figure something out.
The 1901 census gives his name as John.Marie-Anne's marriage record gives him a middle initial "M".You said his name is Jean-Marie, but following traditional Acadian genealogical research, when a person did not have a given middle name in the mid-1800s, his middle initial indicated the first name of his father."M" then would stand for Marc, Marcel or Marcellin, and as I went through the rest of my data, I found a Marcellin Boudreau (s/o Isaie and Rose Boudreau) who married in Bathurst on 4 May 1857 to a Françoise Doucet (parents not given, who had a son Jean born in Petit-Rocher on 23 Apr 1861!!– he too was also 6y in the 1866 parish census of Petit-Rocher and 20y in the 1881 census.Following this traditional way of climbing an Acadian tree, then, I truly believe you want THIS Jean (à Marcellin) Boudreau as the husband of Marguerite Hache, as it is more congruous with the marriage record of his daughter Marie-Anne, who calls him "John M. Boudreau".
Isaie Boudreau was s/o Joseph & Isabelle Bujold; he married Rose Boudreau d/o Cyprien & Francoise Melanson on 6 May 1822 in Bathurst, NB, and desscends from the smaller Boudreau family in the region founded by Athanase & Felicite Orion of Nicolet, QC.