U.S Citizen wanting to travel to Cuba

Greetings,

I am thinking about going to Cuba for 8 days. I will go through Cancun. I have found it to be difficult to book an all-inclusive hotel through a Canadian travel company. I find that they don't return my calls. How should I go about booking my flight and hotel? Is it best to buy the plane ticket in Cancun, and find a hotel once I am in Havanna? Is there any way to book prior to arriving? If so can someone give me the name of a good travel agent that will work with a U.S citizen?

Thank you,
Shaun