Basically you need to get to Cancun through Corozal Belize and then Chetumal Mexico.
Maya Island Air will start flying to Cancun, Guatemala City, and Honduras next month. The airline announced that it is going regional on July 8th. That’s when the airline will begin flying two return trips to Cancun daily and daily roundtrips to San Pedro Sula Honduras and Guatemala City.
Rarely there are flights from Chetumal to Cancun, so you need to get a bus from Chetumal to Cancun. You can fly from San Pedro to Corozal, then take a bus across the border to Chetumal. They have a nice big bus station there with many scheduled busses and several levels of service. The bus system in mexico is very nice. movies, assigned seating, etc... Pick the fanciest its not that much more. There is an all night bus that makes the travel go quicker.
Click below for more information:
How can I get a bus from Mexico to Belize?
That information is for coming the other way, but much is the same.
It takes about 10 hours if you get the nonstop from Chetumal to Cancun.
Travellers heading north can now travel in style as National Transport launched a new luxury service. The Premier Line consists of three buses making three trips from Belize City to Chetumal daily at six, nine, and eleven a.m. Executive Secretary Linda Trejo told News Five what amenities come with the ticket.
Linda Trejo, Executive Secretary, National Transport
“The accommodations are first class air conditioned bus, bathroom facilities, television and trained experienced drivers.”
“We did a couple surveys and we realized that the people are interested in the first class service that we had previously one time ago and we decided that we need to give the people the service that they are requesting.”
“This Premier Line is a premier, it’s an elite line that will not be stopping at no little junction at Pallotti or Biltmore or nowhere. It’s a direct line, Belize to Orange Walk, Orange Walk to Corozal, Corozal to Chetumal.”
That ticket to Chetumal will cost sixteen dollars one way, and thirty-two for a roundtrip. Tickets can be bought upon boarding at the Novelo’s Terminal or at the National Transport office on Magazine Road. Trejo says the company also has plans to introduce the service in Dangriga and Benque Viejo.
Also you can check with George And Esther Moralez at http://gettransfers.com or the Menzie’s at http://belizetransfers.com . They can help you.