Sorry, I was not in a position to answer you query before today. Here is what I have on the subject. There were not many Pierre Garneau - Pierre G. and Catherine MaillotM. 1748 died childless. Pierre-Cyrille G. and Helene Perrault M. 1844 in St-Jacques de Montcalm Pierre G. and Thérese Huot M. L'Ange Gardien in 1724 their son Pierre G. and Marguerite Julien also M. in l'Ange-Gardien in 1763 And their son Pierre G. and Charlotte Lemire M. in L'Ange-Gardien in 1792 The lineage from St-Jacques de Montcalm could interest you. Because this couple migrated to Ellensburg N.Y. abt 1845-50 with family of Jean-Baptiste M. to Luce Belec also daughters Lucie and Flavie
If you could supply me with the date and place of marriage of your mentionned Louis-Joseph with Genevieve Constant probably could be in a position to link the descendance.