I did a little research on Leo and the Anakin role.
Leo was a SW fan and Lucas daughters loved DiCaprio. So Lucas invited him to the ranch in 1999 for a private screening of TPM and then Lucas hung out with Leo all day...
Leo met with Lucas about the role of Anakin, but it was just one meeting and Leo didnt want to do it. In an interview Leo discussed turning down the role. He said "I wasn't ready for that kind of role at that point in my career". This is a line actors use as instructed by their publicist when they actually mean "That script was garbage, no way I want to do that sheet".
Years later, Leo bragged in another interview that he was proud he turned down franchise roles such as Spider-Man & Star Wars.
Ironically Jake Lloyd looks like a young DiCaprio. I think Lucas might have wanted Leo in that role , esp when Spielberg knew Leo pretty well and eventually used him in Catch me if you Can. Spielberg probably also discussed Leo with Lucas. Spielberg also worked with Liam Neeson in his oscar winning film Schindler's List, which was Lucas first choice for the star of TPM. Lucas also had concept art of Ralph Fiennes (also in Schindler's List) as Obi Wan Kenobi - but nothing confirmed he wanted Fiennes.
And although the prequels were god awful films, Leo would have been the absolute no doubt best choice for the role of a young Darth Vader, the most iconic movie character of all time. He had the acting chops, the look and the charisma to nail that role. But Leo is smart or has smart enough ppl to identify what scripts are worth doing because Leo has picked some AMAZING work !! I wasn't even a big fan of the guy, but Romeo + Juliet, Titanic, The Departed, Inception, Blood Diamond, Body of Lies, The Aviator, Gangs of New York, Wolf of Wallstreet, Man in the Iron Mask - the guy RARELY takes on a bad movie !! I even enjoyed The Great Gatsby.