Chetumal across to Corozal, Thunderbolt (boat) to Ambergris Caye then Caye Caulker Water Taxi to Caye Caulker and then onto Belize City. Bus it to Punta Gorga where you can catch a ferry (water taxi) to Puerto Barrios, Guatemala and make your way to Honduras, La Ceiba, Utila, Roatan and Guanaja. Great trip mate!
Of course make lots of stops along the way, great route to see everything.
SIN