Depending upon who gave the census taker the information, you see is what you get.I wouldn't worry about the flip-flop. The ages and siblings coincide.So the probability is high they are the right family despite the mistakes. As you said, sorting it out keeps it interesting.
Sophie/Sophy/Sophia is the parental clue, born about 1823 in Canada.
1870 Champlain, NY: Sophia Lafountain, with children Seymour, Alexander, Zeb, Jane, William, George, Susan and Aka. No husband listed. 1860 Champlain, NY: Seymour Lafountain (35 years b.Canada) and Sophie (33, b.Canada), with children, Seymour, Alexander, Joseph, Sophie.
Some correlation here.So parents could be Seymour Lafountain and Sophia . Not having any luck finding the marriage in Cananada, but it was probably around 1850 if these are the right families.