Under the ‘Buy’ section, they go into a lot of detail, but there are a few key points:
credit cards will not work. Well, they will .. maybe .. if completely unaffiliated with US companies. US credit cards definitely won’t. So don’t rely on those or US bank cards.
Most travellers carry cash. There is however, a 10% penalty on exchanging USD, so convert to CAD (Canadian) or EUR (Euros) first before arriving there.
Do the currency conversions well in advance – the airport may be more expensive.
there are also prepaid / rechargeable payment cards you could organise, but this does take preparation in advance. Some are listed in the article (eg Duales, Telecash)
If you’re returning, you might consider opening a bank account in Cuba – Canadian banks can wire to your account there.