April 22 (Reuters) - Canadian National Railway Co on Thursday sent a letter to Kansas City Southern’s board, saying the company is confident of winning regulatory approvals for its takeover offer of about $33.7 billion. Canadian National submitted its bid for the U.S. company on Tuesday, rivaling an agreement Kansas City already had in place to be taken over for about $25 billion by Canadian Pacific Railway Ltd. (Reporting by Shariq Khan in Bengaluru; Editing by Anil D’Silva)