CBSE 12th

You can pursue B.Tech in computer science and B.Tech in any field you want but I would suggest civil, mechanical and computer science.
You can do BCA also.
Good luck.

Yes, the line you want to choose and it is different for different boards.

Hi,
Please go through the below college predictor you will get to know the details about it.
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

Try NIIT, Amity and LPU. Actually there are many pvt. colleges that consider 12th marks for eligibility criteria. And if you have appeared for JE and you think your rank is low that doesn't mean you can't get any college. But one thing that is for sure is you will not get any govt. college.

No, it's not mandatory.

To join Canada, you need to do a 4 years degree course. You should do graduation in the field where you want to pursue Masters. Remember, if your UG background does not match with your PG subject in Canada you may be rejected. After completing graduation, do a related PG degree or a university PG Diploma.

Hi Nikhil, research will come later, first you complete your bachelor degree in either mechanical or automobile engineering to understand the field. Gain some work experience. You must then go for a integrated M.Sc/Ph.D or simply a M.Sc and then a Ph.D.

You can opt BCA or B.Sc IT or B.Tech CSE.

Hello Bhoplu, please complete your Bachelors degree or a job oriented course in an area of your choice. The higher your qualification better the chances will be.
With class 12 qualification job opportunities will be limited to very novice jobs or you can check government jobs like
Lower Division Clerk
Postal Assistant
Data Entry Operator
SSC Stenographer
Railway clerks and constables
Ticket collector
Assistant loco pilot
Indian Coast Guard
Indian Navy
Indian Army
Take UPSC or SSC exams.