Is parking available near the pontoons?
There are various carparks near the Portello pontoon in Padua which are marked on the map (last page of the PDF): http://www.ilburchiello.it/public/sitemin/Come_arrivare_ai_pontili_di_imbarco.pdf
You can make use of the carpark next to the Villa Pisani in Stra (see map). Once the cruise is over, you can return to collect your car by ACTV bus.
In Oriago you can park at the Il Burchiello restaurant; once the cruise is over, you can return to collect your car by ACTV bus.