If walking distances is a problem you may want to consider a private tour.
You are not pushed to keep up with the bus tour and can tour at your own pace.
I am sure the crew could get your scooter on the tender without any problem.
We had a lady with us on tour in a wheelchair and she managed the tender fine.
Alexandr Pushkin, Carnival-Holiday, HAL-(old)Westerdam, Orient lines-Marco Polo, Royal Olympic-Olympic, NCL-Dream, Dawn-Princess, ACCL-Grande Caribe, Oceania-Insignia (3), Regatta(4) Marina (1) St Lawrence Cruise Lines-Canadian Empress
Scenic River cruise June 11,2012