I've searched all the birth and marriage records for Nice and found nothing for Charles or his children. I found a couple of Huards in Nice who came from Brignoles in Var so I looked them up but there was no connection with Charles.
I did find a baptism for Eulalie Gautier on 25 March 1852 in Saint-Dominique parish daughter of Horace and Elisabeth Lupia - is that your great-great-grandmother? What information do you have for her? Do you know in which parish or commune of Nice she and her ancestors lived? That can sometimes give some clues. Quite often marriages took place in the wife's parish. Do you know what Charles's occupation was?
Let me know any information you have on Charles and Eulalie up to their arrival in Canada. If you ever heard any names of people or places, no matter how vague, let me know and I'll see what I can do to help.