What cruise line are you going to be on?
Most cruise lines have wheelchair assistance (their wheelchair) for embarkation and disembarkation. There are personnel who push the wheelchairs for you. Such as, for embarkation you can get pushed, using the ship's wheelchair, from close to the entry to the terminal, through check-in and security, and to wherever you want to be dropped off on the ship (like your room if it's ready or the buffet, etc). These same wheelchair pushers will push someone who has their own wheelchair, too. Once they drop you off inside the ship, they will take the wheelchair (if it belongs to the ship) with them.
If you rent a wheelchair from Scootaround or Special Needs at Sea, it will either be waiting for you outside the terminal or inside your stateroom (depending on where the ship departs from).