the simplest way,

CSE = software + somehardware

ECE = somehardware + morehardware

software = {normal C,C++,Java programming, OS, web development, machine learning, AI}

somehardware = {microprocessors, microcontrollers, computer architecture, some aspects of computer networks}

morehardware = {control systems, antenna theory etc etc}

I think this will give you a somewhat basic idea about the similarities and differences between CSE and ECE.

Now coming to the second part of your question,

Career opportunities for a BTech in CSE:

• Considering that you're able to maintain a decent CGPA from a decent engineering college, then be rest assured, you'll get placed in mass companies like TCS, CTS and Infosys.
• Considering that you have an active interest in webdev, machine learning and AI and have also done relevant projects and other work(building cool stuffs) in that field/domain but you're not interested in pursuing higher studies, then it will still be easy for you to get jobs in startups and other core companies. (They will also pay you a handsome package, Dont worry)
• Considering that you're passionate about CS and you're quite willing to do higher studies, then appear for GRE, get a good score and go abroad. After MS, you really wont have to think about getting a good job.

Career opportunities for a BTech in ECE:

• Same as the first point above, if you're able to maintain a decent CGPA from a decent college, you'll get placed in mass companies.
• If you really like your subject and have built some really cool stuffs, then it will still be not that easy for you to get a good jobbecause selections are quite less as compared to CSE whereas competetion is tough.
• So the only viable option left for you is to do higher studies(GATE, GRE). Oh, yeah, you can also appear for IES examination. That's an advantage if you're looking forward to work in the government sector.