We were on the August 29th cruise which covered NE/Canada. No a problem whatsoever for someone in a wheelchair. My wife had her hip operated and basically need the wheelchair to move around the ship. No problems in any or the restaurants or the theatre. In the theatre, there's rows especially reserved for wheel chairs. We had a balcony view cabin and the manual wheelchair fit the entry way with a mere inches to spare. The toilet is what we call "elongated" and my wife had no problem sitting and getting up. The shower is small as there's no way to fall.
During the day we spent our time in the Solarium and enjoyed the solitude. We also took advantage of "North Star" the day we ported in St John. They transferred my wife form her wheelchair to one of theirs and rode the elevator to the North Star.
RCL staff was ever so helpful on board and also in getting my wife and her wheelchair on and off the ship in the port of calls.
You should check your cruise planner if interested in any tours. We used RCL for tours in Boston and Bar Harbor. As mentioned, RCL staff was friendly and helpful in helping us get on/off the ship. Likewise, the tour bus drivers were prompt in having the wheel chair ready available at each stop. One of our tour in Boston was the Cape Cod tour and one of the stops was a boat ride of the Hyannis Port and the Kennedy compound. It was amazing how the boat crew member navigating up this sloped ramp of about 15 feet in getting my wife and wheel chair on/off the boat. Same experience in Bar Harbor tour of Acadia National Park and later a lobster dinner at a restaurant in town.
Also, be sure to sign up for disembarkation time assigned for those in wheelchairs/mobility problems. We were assigned 7:30 AM and met by Jamie's Italian restaurant. At the approximate time staff members of both RCL and some working for the Port (?) met us and an individual was assigned to each of us and left the ship in a parade like environment. Bayonne Customs/Security uses Facial Recognition Technology and it took us no more than 20 minutes to disembark, get our luggage, clear Customs and on to the garage.
Ps. Enjoy the cruise.