Part of Can Tho's charm is that there isn't a lot to do. The city practically forces you into a state of relaxation; it's hard to stress about "seeing all the sights", when there aren't many sights to see. The entire itinerary for our first day was "Boat Ride", so when the tour turned out to be six hours long, we didn't mind.
It's unavoidable. If you plan on spending any time on the Mekong Delta, you're going to be taking a boat trip. Who visits the Mekong and doesn't take a boat trip? And it's just as unavoidable that, unless you're willing to invest a lot of money, your trip will be pretty touristy. But that doesn't mean it can't also be fun.
For about a week, hundreds of boats from the Mekong Delta line up along the Ben Binh Wharf to sell the flowers and small fruit trees with which Vietnamese families decorate their homes during the holiday of Tet. Visiting this floating flower market was among the first things we did in Saigon, and the scene made a huge impression on us.