If Harry Kane wants to win the Champions League title, he will probably choose the Bayern Munich team. Because Bayern Munich can dominate more than Manchester United in the Champions League. However, Manchester United is a strong enough team. Bayern Munich and United are not weak teams. But first Harry Kane should be without Tottenham. However, since Harry Kane has played in the Premier League for a long time, Harry Kane could probably adapt quickly to any Premier League team.
Can't guarantee with Bayern Munich have bigger chance winning Champion League than Manchester United next season, actually Bayern have experienced than Manchester United but Primer League teams always dominance in Champion League than Bundesliga teams. Harry Kane not answering yet about his future team, stay with Tottenham Hotspur but forget to play in Champion League next season because Spurs play in Europe League or joining with Manchester United or Bayern Munich.
Not difference between Primer League or Bundesliga, I think Harry Kane will adapt well if agree joining with Bayern Munich or stay in Primer League by accepting Manchester United proposal.