I am very sorry but I fail to see why two of Alexis Gagné's wives who are second cousins would require a dispensation. It is not uncommon to have a man married to two sisters who do not require dispensation.
Register entry says « ... san_ aut___ empèchement ni opposition entre Aléxis Gasnier dit Belavance veuf de M. Josephe Soulard d'une part et M. Madeleine Pelletier fille de feu François Pelletier et de défunte Genevieve Morno d'autre part ... »
That clearly says the dispensation applies to the link between Aléxis and Madeleine—not to the link between Madeleine and Josephe. No?