No, US airlines or their third party agency sell tourist cards by mail or at the gate. Depending on the airline and method of purchase, the PINK tourist card (for those departing from US ports or airports) sells for U$50-U$100. Check with your airline after ticket purchase for details. Usually they contact you.
You should decide which of the OFAC categories is your reason for travel to Cuba, because you will be asked by the airline to declare it.

You may not even be asked, when entering the US from Cuba, what you were doing in Cuba. However, since you are subject to US law, and US law does not permit travel for tourism/pleasure, it doesn't seem wise to say that. You will be asked to declare your OFAC reason for travel at departure, so if asked on return to the US, that is what to say.
On entry from Canada to the US to get your flight out to Cuba, why say more than you need to, if/when asked, that you are visiting the US to travel the US.