I went via CFCJ in Toronto. Flew from NYC via YYZ.
We flew with about 8 giant suitcases filled with all types of stuff for Pesach and to distribute packages to the Jewish community.
I decided to risk a few vacuum packages of meat which luckily made it thru. Other than meat they wouldn't care to let me bring in pretty much any other food. (we brought in wine, which they decided to allow, milk, tuna, bread etc.)
Convinced the customs that we were a couple going on a honeymoon and needed to bring all our stuff because of Kosher laws. (Friend of mine went in with a case of Gefilte Fish and told them he eats only that, 3 times a day for a month...) got in without trouble, they already know american's can't get a stamp in their passport, but if you aren't american, make sure to tell them not to stamp. They did make me buy some sort of medical insurance plan (a few bucks a day) because US banks, insurance or CCs aren't acceptable there. (this may change based on the latest news). I would suggest to divide up and hide your cash you bring in, in case they have trouble with it etc. Bribes are not allowed, so if you have trouble at customs, they will more likely accept your offer of some of your american food than risk accepting cash, so don't try that. People are really nice, including the guards.
In Cuba there are two currencies, one for locals (CUP?) which is close to worthless, and CUC for foreigners, which is more than 1 USD to the CUC. Taxi drivers and everything else will only accept CUC.
We stayed in a "Casa Particular" in Havana, which is kind of like AirBNB. Basically many people in Cuba rent out the main part of their house, furnished, prices weren't super cheap. These arrangements were made by CFCJ beforehand. There are some nice hotels in Havana, all government owned, but to american standards I believe. We would go to Hotel Melia Cohiba for the WiFi, which was slow, and $14 CUP for 2 hours.
We went primarily to deliver packages to all the Jewish families before Pesach, and to make Sedorim. There are a few functioning Shuls in Havana, one of which I believe may be officially Orthodox. There are signs pointing them out for tourists, we did not risk going there, as the people in charge of the Jewish community there with government connections, have had fallings out over the years with CFCJ (at least in part because they know we don't recognize the conversion of some of the prominent people in the community as Jewish, due to their non Halachic conversion).
Bring food with you, as you can't rely on much being available, even for money. (We spent 2 days looking for an apple for Charoises). There might be some fresh fish available, but it tasted horrible. Eggs, potatoes, tomatoes, bananas, eggplant, cucumber are some of what was available. (people did not know what a hot pepper was).
Always haggle on taxi prices, or souvenirs. In stores prices are generally regulated and marked.
Old Havana is really beautiful. There is a Rum factory which has tours, did not get to check it out. There is a Cigar factory which is only open in the morning hours, also did not get to it. There are plenty beautiful beaches only 20 minute drive from Havana, which you can find relatively empty patches on. You can see the particles of white sand thru the crystal clear blue water. (I have not been to some of the other places out there to compare, but Cuba is legendary for the beaches). Some of the nicest beaches there is in the next city Varadero, like 1.5 hours, and also has hotels and many shops with many foreigners and foreigner prices.
Personally I mainly enjoyed the local culture over the tourist traps. So just walking down streets, is an experience. Literally go back in time a few decades.
People on the street don't all smoke cigars, as they can't afford it. Every guy is ready to hook you up with "brand name" cigars his "brother/friend got from the truck/factory". You can buy proper ones from any normal looking cigar shop or lounge and in the nice hotels.
According to the US, you are still not allowed to go for vacation, but you can go for a number of other reasons: journalism, culture, humanitarian etc. So if you can go legally by applying for permission from the US, go ahead. otherwise you risk the chance of US customs catching you coming back from canada, in which case you will need to fill out the paperwork of what you went for, who paid for your trip and expenses while there etc. Nothing is allowed to be brought back in (don't know yet how this might change) so anything that said cuba on it, was destroyed in front of me, and I had to sign that I witnessed it.
There are awesome cars from the 50s, 60s and 70s all over the place. the taxi drivers will try to get extra for a ride, knowing it is a thrill for foreigners. Did not drive one, but did take some rides in them.

The local people can really use the food, so please please bring extra if you are going on your own, and give everything to them when you are done with it. (We served some fried eggplant with a drop of may on top by the Seder, and the people were all excited "how healthy it is" because it contains nutrition. They live on the equivalent of $30 USD a month, regardless of occupation. Unless you are retired, then you get about 11/12. They have little ration books "la librita" which entitles them to a certain amount of certain foods at a discounted rate (read: affordable on their salary). About 1/4 of a chicken per family per 10 days. A certain amount of rice and eggs and bread and milk etc. So with money you can buy as much as you would like. (If you can get a local to do the shopping for those foods for you, it is in the cheaper currency, and won't be extra price for you).