I am not sure if you are still interested in Modeste Garneau, but I can give you some info. Modeste was the son of Joseph and Geneviève Sévigny. He married three times and had kids from each marriage.
He first married Madeleine Coté in St-Antoine de Tilly (20 nov 1843. Charles, my great grand father, was the only child reachind adulthood.
He then became protestant and married Elisabeth Mitchell inIreland township (Mégantic, Québec) on 14 May 1850. They had six children including William Mitchell. She died shortly after giving birth to her last daughter Elizabeth Jane on Dec 27, 1862. Modeste remarried a third time with Hannah McKnight Phoenix on Feb. 7 1865. They had four children, but only three survived. Modeste died Jan 6 1872 in Ireland township (Mégantic, Québec) and lied in the nearby Maple groveAnglican cimetery.
If you have any information about William (wife,marriage location, time of arrival in the state, occupation, etc...), I would be interested.