If you have thought about getting over to Cuba before things really change, you are not alone. Despite U.S. policies discouraging U.S. citizens to visit Cuba, each year more and more visitors from all parts of the world discover the charm of this hidden Caribbean Island and it's warm people.
Cuba as it is today will not exist once the floodgates of U.S. tourism open, and that could happen very soon. Papa (Castro) appears to be on his last leg (pun intended) and things in Cuba will change significantly after his demise.
Cancun is a popular gateway to the island Country of Cuba, and is a very real alternative to the tried and true gateway to Cuba via Canada. There are direct flights from Cancun International Airport, and the fares are very competitive.
Yes it is illegal for US citizens to travel to and spend money in Cuba without US government approval. To avoid getting caught, most gringos who sneak a peak at Cuba do not get their passports stamped, reducing the possibility of getting caught when flying home from Cancun on the return trip.
Yes the risk is still there, and yes you must lie to the US Immigration officials if they ask you if you have been to any other destinations in addition to Mexico. It's your call.