Mexicali IS in Baja California. Actually, such city is the capital of the Baja California state.
If you mean what body of water is between Baja California and the Mexican mainland, that would be the Sea of Cortes or Gulf of California. See related questions for further detail.
The Rio Grande
Translated Big River
Gulf of California is a place in North America. It is an inlet of sea-water between the Mexican Peninsula of Baja California and the Mexican Mainland. See the linked Wikipedia page for more information.
Gulf of California
No. The Gulf of California is a body of water on the west of Mexico which separates the Baja California Peninsula (south of the US state of California) from the mainland Mexico. The Gulf of Mexico is on the southeastern US and east of Mexico, and US states such as Florida, Louisiana and Texas have shores on that body of water.
The Gulf of Mexico, the Pacific Ocean and the Gulf of California.
Golf of Mexico
The two bodies of water that border the coasts of Mexico are the Gulf of Mexico and the Gulf of California. The Gulf of Mexico is part of the Atlantic Ocean while the Gulf of California is part of the Pacific Ocean.
The Gulf of Mexico lies between the Florida Peninsula and Mexico.
It is the Gulf of California.
The Yucatan Channel is the strip of water provides a passageway between Mexico and Cuba.
The Gulf of Mexico is bigger.
Mexico
The Atlantic Ocean, the Sargasso Sea, the Caribbean Sea, and the Gulf of Mexico are the water bodies that are between Spain and Mexico.