It doesn't matter course you choose as both are almost similar However if you are stuck for choice then go for B.com it has some aspects of banking that you could learn. And there is no direct route to become a bank manager. Once you graduate you can join a bank directly or by giving exams (preferably PO exam) and if promoted later you could go up to managerial positions.

I hope you got my point. All the very best for your future endeavors!