First, you won't have any problems with Cuba or Canada doing this as a US citizen, it's of course the US where you could have problems
Education type permission is pretty easy to get for Cuba (eg teaching, study abroad, anything museum related, etc.) and I believe they can cover a spouse. The fact that your husband is Canadian makes it more complicated I assume. There are companies that specialize in Cuba visas - contact one of them and see if such a spousal arrangement is possible given that your husband will be there for educational reasons. Another option would be to explore study or educational (eg volunteer at a museum) opportunities yourself to get legal permission to go there.
The less legal option is to just go and not tell the US government. It's hardly unusual for someone with a Canadian husband to spend month in Canada and the US immigration isn't going to question it - though maybe let the tan fade before you cross back
Finally, technically the law is that you're prohibit to spend money in Cuba or on travel to Cuba, so on the almost 0% chance you get caught it might just turn out that your controlling Canadian husband handled all of the finances and certainly that none of the funds you spent there originated in the US!