US$ is used in Cuba. It may be possible to cash American Travelers Cheques but only at the bank. Travelers Cheques drawn on a Canadian bank are more convenient.
You may receive some ‘convertible’ peso coins or notes. These have the exact same value as US money and should be spent or exchanged for US money before leaving Cuba.

It is not illegal to use Cuban pesos however, you will be expected to pay in US$ if you are a visitor to Cuba.Cuba decided to open up to tourism due to the need for US$ exacerbated by the blockade.Since we are not paid in pesos it seems reasonable to most travellers that we use the currency most needed by Cuba.