I agree with the two gents, get a private water taxi to the hotel. It is a lovely experience, very James Bond!!! You can get a water taxi without booking beforehand, just follow the signs / path from the airport to the water taxi rank!
Either a water taxi... or we used Alilaguna Blue line... the Zitelle stop is literally a minute from the hotel entrance. Have a look at their web site; you can buy tickets online... (you have to swap the online voucher for an actual ticket at a booth next to the jetty) It is slower than the water taxi, as it is making stops, but what's the rush? Also, a tip for a good lunch restaurant on the Giudecca...is the "Palanca" it's a small place but the food was very good and there's a great view towards St Marks Sq from the canal side tables. Have fun.