I dont think Barcelona and Real Madrid will be a good place for Kane to play. Competition against other players to take the main position is so hard on both team. He will be only like Pacacer in Barcelona or Morata in Real Madrid which is not good for his career.
There may be some place for kane in real madrid. We all know that benzema is old now and he will probably play for a maximum of 5 years to go so it is not impossible for them to sign kane and let him play alongside as a substitute atleast for now. Kane is still a young player and one of the most brilliant striker in premier league
Kane wants to be a great footballer, he will learn from the mistakes of Bale and stay in England, If he goes to madrid then he will just be "that dude that plays beside ronaldo" If Kane is to leave totenham, I think he'll leave for Man U or even chelsea