Hi Cricket, I went and looked up the 1871 Ontario census to see what I could find for you. In the county of Prescott in the Township of Longueuil on Pg. 2 District 75, I found
Joseph Sauve-male 26 yrs. born in Ontario(this would give him a birth year around 1845), Farm Labourer married in October of the last 12 months,(which I presume means he married Harriett in October 1870). Harriett-female, 20 yrs. born in Ontario.
Now the only thing I find a bit confusing is that Harriett is listed as SCOTCH, which could be an error. I think this must be your great grandparents(and my great great Grandmother Harriet).They would have been married the October before,(I think the census was in the summer of 1871) and little Louis Edmond is born in the fall of 1871 after the census and therefore is not listed. Now if this is the Joseph and Harriet we were looking for we can now look for a wedding in October of 1870 likely in Ontario since they were both apparently born in Ontario??? I also see folks that could be Harriet's relatives in the same area under the name Roulleau(intstead of Rollin). It also appears that Sauve could be Sophy/Sova/Sovey/Sovie and that it sometimes goes by the dit name "Laplante". We will solve this one yet!