My 3GRGU (Grand Uncle) went by Denis for a time Too.

On the way to establishing the ancestry of my 3GRGR, I wound my way through the men who we believed were his brothers, including Julian LaPorte.  The Pontbriand marriage book (Marriages (1830-1880) Comte de Clinton (New York), contained numerous entries for Julian's daughters. In it, his wife was consistently referred to as Sophie Roy.

So, I did some digging with the new "Denis" lead and found his (Julian Denis's) marriage record to Sophie Roy.  Julian Denis was also the son of Charles Denis and Marie Guenet. My French is horrible and the record from ancestry.com is a bit rough, but you can very easily make out:  Julien Denis marrying Sophie Roy and the parents of Julian being "Charles Denis" (fifth and sixth lines) and "Marie Guenet" (sixth line).  The parents of Sophie Roy look to be "Joseph Roy" and "Francoise Leblane" (? don't know on that last name).

Circumstantial evidence supports that Julius and Julian were brothers, including living next door to one another at least in the 1850 Census period, that Charles and Marie had two sons named "Julien" born in 1810 and 1815 respectively, which ROUGHLY coincide with birth years for both of them, and also that there is a reference in Julius LaPorte's pension file. In it, there is a question about whether Julius and his fifth wife, Mary / Rachel / Cecelia / Miro, owned property.  Clinton County records apparently showed ownership by "Julius LaPorte."  The pension file indicates that the Julius in question is my 3GRGR's "nephew." (the explanation spills over to the text written on its side).

From census records, we know that Julian had a son named Julius:

Julian's marriage record is more helpful in this regard than Julius's because the latter were married in the United States and that record mentions only the bride and groom and no ancestors.