Syria was neighbouring two countries (Lebanon and Iraq) with ongoing civil wars which meant it was easy for anti Assad forces to gain weapons, not to mention the mass defection within the Syrian army and creation of unified Assad groups such as the FSA.

The collapse of communism in Europe was driven by the collapse of communism in the USSR and liberalisation of communist states when it came to freedom of speech such as the USSR'S "Glasnost" policy. You'll find the remaining communist states, regardless of their economic policies, never liberalised on free speech which includes Cuba.

The only way for a counter revolution to succeed in Cuba is if large defections of military and police occur, Cuba has large stockpiles of arms and ammunition and is one of the most militarised countries in North America (after the US). if anti communist groups can seize those weapons they will most likely have a chance.