Can a Canadian marry a U.S. citizen while on a visitor's visa?

Yes. Theer is nothing to prevent anone from getting married in US, however BICE sees this a atempting to immigrate into US.

Yes, you can merry after 60 days. Now the intent to migrate to states is upon the immigration to prove that u came to u.s to get married. but if u get married before 60 days of entering the states then the intent is upon you to prove that u did not came here to merry. makes a huge difference when they immigration person have to prove your intent.