Kane and Mbappe are probably good options for Madrid in their search for a replacement for Benzema. but it seems the current rumors are looking far away for Madrid to get both, or one of them.
Kane seems more interested in Man United. while Mbappe I don't think will leave PSG after they lost several important players in the squad.
Madrid must find another alternative if they do not want to be left behind by City. this season Madrid is lagging behind City and they have to catch up with several player transfers. if not next season City could have dominated again in Europe.
Harry Kane is the best option for replacing Karim Benzema position in Real Madrid, but not sure between Madrid and Spur reach agreement about how much transfer values. No doubt Tottenham Hotspur always made difficult for signing Harry Kane regarding last two season Manchester City offering above 100 million euro denied and City move their target for Haaland.
Real Madrid have one step forward for signing new player fill position leaving by Karim Benzema, between Mbappe or Harry Kane as the best choose right now and Madrid should get signing Kane or Mbappe, but if failed to sign Mbappe whether want it or not Madrid have to give excited offering for signing Harry Kane from Tottenham Hotspur.
I think Real Madrid made a big mistake by not focusing on La Liga. Because they didn't do anything great in the Champions League, if they could have done the hard work in the Champions League, the team would have had a chance to secure the title.