The expansion could potentially include new lands in Disney's two existing Anaheim parks and a new shopping, hotel and dining district.
The dueling waterslides will first debut for passholders on April 1 and 2.
The parks have not been open with rides or attractions since March 2020.
Disney CEO Bob Chapek said the resort will need time to call back and retrain thousands of Disneyland employees.
Gov. Gavin Newsom's team visited Disney World weeks before issuing guidelines that have kept California theme parks closed.
The event will start March 18 and run on select dates through April 5.
The rest of the Grand Californian and Disneyland's other two on-site hotels will remain closed.