i agree with Michigan about the monorail (and the accessible entrances too). The ramp is basically a long, steep hill that takes you up to the level of the monorail (2nd floor + level).
Previously, the boat dock was sometimes not accessible to guests using wheelchairs because of differences in water levels. Safari Steve (a MK CM) recently posted that the boat docks have been replaced and are now always accessible. The down side id that he said there is now a ramp to the docks. I haven't seen it, but the ramp to the docks would be nowhere near as high as the ramp to the monorail.
If you are staying on site, riding the bus to MK works out best. The bus drops you off right by the turnstiles, avoiding the issue of the monorail all together.