From the cruise terminal you can easily reach Piazzale Roma by taking the “People Mover”. From there you may take line 2 of the ACTV (ferryboat) and disembark at Rialto stop.*
*From Rialto pier, you may continue walking along Calle Larga Mazzini, turn at the intersection with the second street to the left (“Calle dei Stagneri”), go on and turn to the first street on the right, cross the bridge and you will immediately find “Ai Reali” Hotel.