There is a main bus terminal in Corozal. It's on the main highway, and about a 2 minute walk from the center of town.
But, what "luxury" bus are you taking?
The Premier Bus Line (Belizean) and all the other Belizean buses will stop at the terminal, but the Linea Dorada and San Juan buses don't stop in Corozal anymore.
Here's my site with bus information: http://belizebus.wordpress.com/
I had a quick look for a map of Corozal Town.
http://www.northernbelize.com/map_cortwn.html
The red line is the main highway. Look for the number 1 in a circle. The bus terminal is on the upper left side of the circled number 1, on the curve in the highway.