Francois-Xavier Guimond who was married to Marguerite Bernier is not the same Francois-Xavier Guimond who was born in 1750 and baptised 17 June 1750. The Francois-Xavier Guimond married to Marguerite Bernier was indeed the son of Jean-Gabriel Guimond and Reine-Ursule Lemieux.
Jean-Gabriel Guimond was born 21 November 1739, Cap-St-Ignace, Quebec, married 10 April 1763 Cap-St-Ignace to as stated Reine-Ursule Lemieux, she was born 28 April 1743 Capt-St-Ignace d/o Louis Lemieux and Louise Gamache.
Jean-Gabriel Guimond was the son of Louis Guimond & Ursule Bernier. Hope it is a help to you.