Every situation is unique and because we trade with China dosen't mean we have to lift the embargo with Cuba as long as there is a Dictatorship.
What the Cuban people (I'm one of them) need is the same freedoms that we have here in the U.S. By lifting the embargo without guarantees of human rights and freedom to Cubans, all is going to do is to strenghten the Castro regime, and the Cuban people will still be opressed under their Communist system.
Look at your example of China , we trade with China,and they have a world economy now. They even have Triilions of Dollars of our debt in the U.S., but the Chinese people are still opressed. That's not right. That's not what we Cubans want. We have suffered 50 years of dictatorship and what we want is the same freedom as you have in the U.S.
First, I think everyone would agree that Cubans deserve and would love to have the freedoms we do in the U.S. However, the embargo is not going to help them get those freedoms.
Historically, economic embargoes have not had much success at trying to create change in the embargoed country. This is even more true with unilateral embargoes such as the U.S. against Cuba, regardless of how powerful the country instituting the embargo is is. Even in modern cases, such as North Korea, Iran, and Sudan, economic sanctions/embargoes have had zero success in furthering political goals. In almost all cases (specifically the three countries mentioned above), the embargoes have done nothing for the people of the country except make them worse off and have helped or at the very least maintained the status quo for their leaders. Take Iraq under Saddam. He maintained a stranglehold on power and lived in opulence while the people of his country died due to economic sanctions. Same with North Korea; Kim lives the high life while millions die from starvation.
Trade, on the other hand, has a great track record at promoting change in countries. China is a great example of this. Before finally joining the WTO in 2001, China had to clean up its act, both economically and in the human rights front. I'm not saying China is perfect or doesn't still have levels of oppression that are disgusting, but it is much, MUCH better now than in the past several decades. There is now a thriving middle class in China that wasn't there before and they have some political freedoms like local elections and limited freedom of speech and press. Its a slow process, but one that is only possible with trade and engagement.
With trade, you can assert leverage over a country in a way that is impossible to do without a trading relationship. Trade doesn't solve everything, but what is a better way to promote your country's values and ideals than to sell your goods and ideas to other cultures? Ending the embargo would not only benefit Cubans economically, but also start the process of opening up the country politically. Not all evolution requires revolution is the phase that comes to mind; Cuba won't change overnight with the embargo lifted, but Cubans stand a much better chance of getting the freedoms they want without the embargo than with it.