I booked half the boat for a large group. Tickets were easy to book in advance, and we were able to book either the whole rooftop outside deck with ample notice, or half the group inside and half outside. Depending on the weather, the upper deck may be wonderfully sunny with little shady areas or a bit too cool with the wind. Food and drink service is offered, but a bit too expensive for my tastes.  The guided tour of the water is a perfect afternoon activity to learn more about Habitat 67, Montreal history and offered in french and english.  HIghly recommended if the weather is nice and you've got an afternoon to spend in the lovely parts of Old Montreal.