The title comes from the phrase "A man, a plan, a canal, Panama", a well-known palindrome (a phrase that reads the same forwards or backwards.) It refers to the many plans in this episode that "move backwards" and go awry (Nucky's plan to stage a hit on Joe Masseria, Margaret's plan to run away with Owen, Van Alden's plan to sell alcohol on the side).
Margaret sings to the children in bed "I' See You In My Dreams'. Which is also the song for the closing credits. The scene was 1923 though the song was not written until 1924