Like any other checkride, your seaplane checkride will consist of an Oral Exam and Flight Test. Expect the oral to be under 90 minutes and the flight to around 1.0 or so on the hobbs, of course depending on how far you have to travel to get to the bodies of water you want to reach.
The video above covers what you can expect on your oral and on the debrief, and the video below covers what you can expect on your checkride. To know exactly what maneuvers you will be performing on your checkride, reference the latest copy of the ACS (airman certification standards).