Which are then best colleges in India to pursue BCA and MCA? How can I study ethical hacker (CEH)? What is the scope?

Both the courses have different curriculum! You can do CEH in summer training while doing BCA or MCA. It boosts your career! Good luck!

In place of theoretical courses, it will be better to get practical hands on training experience, so that you have the required skills to start a career in this domain. CSSRL is a cyber security workforce development company which provide such training.