Hi! I wasn't having much luck searching the civil records for Cannes so decided to try the earliest census done in 1872. I found a Jean Salamito, a farmer, his wife Marguerite Donat, and their family including son Louis who is just the right age. They lived at 4 Rue d'Antibes. Where did you get the 1830-1875 dates for Jean Salamito?
I found the birth documents for the two youngest children with the spelling Saramito. Since Jean could not read or write the spelling is left up to the person recording the information. I couldn't find any records for the older children, including Louis, or a marriage document for Jean and Marguerite, which makes me suspect that they didn't live in Cannes then. They could have lived anywhere in the surrounding area.
Jean's age is different from yours, and changes in the census and on the two children's birth documents. All of this is very common: ages change from document to document and name are spelled differently. There's only a few Salamito/Saramito families in Cannes and they all spell their names differently from document to document: Salamito, Salomito, Salamite, Salamitto, Saramito, Saramite.
I was able to find a few more sailings for Louis but so far not the one when he moved to Australia. I found some information on his wife's (Alice Allen) family. I was also able to find their daughter (Alice Samalito)listed on a sailing from London to Wellington in 1913/14 and then sailing from Wellington to Sidney in 1916.
I put all this together into a family tree so you can compare it to yours. Here's the URL for Jean Salamito:
http://trees.ancestry.com/tree/17548337/person/524399298 If you click on "1 Source Citation" next to his Birth it will show you the information that was on the census.
Hope this is helpful.