Here’s The Three Musketeers pressbook portion that covered advertising. “The Three Musketeers was an extremely personal project for [Gene] Kelly for two reasons” (from the TCM article on the movie). “The first was the fact that he was recreating the character (D’Artagnan) played by his favorite star (Douglas Fairbanks) in his favorite movie (the 1921 version of The Three Musketeers). Kelly was later quoted in Tony Thomas’ The Films of Gene Kelly: Song and Dance saying “I loved playing this part. As a boy I idolized Fairbanks, Sr. and I raised myself to be a gymnast.” The second reason is that Kelly was hoping his performance in The Three Musketeers would convince MGM to let him do a musical version of Edmond Rostand’s Cyrano De Bergerac.. Regardless of his energetic performance in The Three Musketeers, the studio brass wouldn’t go for a musical Cyrano even though Kelly pestered them for years about it.”
The TCM article goes on to say how much June Allyson disliked playing the period piece. Lana Turner also had issues with her role as it was not a starring one. After a brief suspension by MGM and a rewrite of her character, she did eventually acquiesce.