If you are traveling on a tight budget, and/or want a more personalized experience, I highly recommend staying at least some of the time in a casa particular. Apparently this term only applies to facilities in Cuba, and a casa is roughly equivalent to a Bed-and-Breakfast Inn. The owner’s family usually lives in another part of the house, which can be quite large. Some are restored mansions from the 1800’s.
There are several good websites you can use to research places to stay. Three that I especially recommend are: www.CasaParticular.Info, www.CasaParticularCuba.org, and www.Connect2Cuba.com. A particular casa particular may be found on several sites. You will find photos, maps, booking applications, suggestions, links, ratings, and other information. You should be able to find a clean, safe room for two for about $25 USD or more per night. Be sure to convert various prices to the same currency to compare rates. Currently $1 USD = $0.90 Canadian dollars, $0.87 CUC’s Cuban Convertible Pesos), and € 0.73 (Euros).
I haven’t yet located any casas where you can reserve rooms on an American credit card via a third country, but I suspect it’s possible. Most simply ask you to just bring cash. Keep in mind that if you reserve a room during a busy season without using a credit card, don’t be surprised if it is not available when you arrive. However, the owner will be able to locate a similar room nearby. Another strategy is to book your first 2 nights in a hotel through a Canadian travel agency such as Nash Travel www.NashTravel.com (where you can also book and pay for your flights from Cancun or Mexico City to Havana and back). Then you can spend some time during your first few days checking out casas during the day. Be sure to clarify if the indicated rate is per room (it usually is) or per person, if breakfast is included (it usually is), and the additional cost for a home-cooked dinner. I suggest only booking 2 nights at a time; then extend day-to-day if you are happy with the arrangements. If you are traveling to other areas of Cuba, your host will be able to suggest casas you could stay at. (I would still go online and check their ratings.)
I think it is really important for first-time visitors to Havana to spend their first few nights in the geographic area known as Old Havana (whether you are staying in a casa or a hotel). There is much to see and do in this concentrated area, which is roughly the area from the narrow harbor entrance and the passenger ship terminals west along Brasil Street to the Capitolio (Capitol Building); north along Prado (Avenue) to the Malecon Seawall, then east and southeast along the Malecon back to the ship terminals. It’s fun to wander around this area at night (particularly along Obispo Street), listening to a variety of high-quality music.
I usually suggest Cuba visitors travel in a group tour on their first trip. There is so much to see and experience. They will likely want to return to Cuba anyway. But if you have limited funds and speak basic Spanish, staying in casas particulares may just be right for you.