Maths

It is very rare to get admission in Science after commerce stream, Science stream student can do Commerce course but Commerce student not. Basically, to be eligible for B.Sc. You should pass from PCB/PCM in 12th with aggregate 50% score from any affiliated School/College.

If you are sure about your choice you may go with arts as it gives more time for IAS preparations. If you go with Science and the graduation from engineering or any graduation you will land up with a safe and strong backup as well.

No, not at all. You can go with Biology or even arts subjects. Even its said that Biology is easy to attempt in civil exams than Maths. Good luck.

With PCB, you can go for B.Sc. This will give you a great scope and exposure. It is not compulsory to take math.

Maths and economic of class 11th are competitively easier than that of 12th. This is because the 11th class math is basic its a kind of introduction and basics. If your basics are clear and strong class 12th will be application and a quite easier for you.

The only way to score marks in Maths and economics is to practice. Both the subjects need a lot of practice. Solve as much as previous years paper and understand the type of question and the values will definitely vary. Study at the most productive time of the day. Depending upon your comfort.

For taking up any branch of engineering it is mandatory to take Science in class 12. or do Polytechnic and then join 2nd year. As with commerce, you can't do engineering.

Some universities and courses for commerce student without Maths in Canada are:
Humber College.
Durham College.
Nova Scotia Community College.
Mohawk College.
CTS Canadian Career College.
Algonquin Careers Academy.
University of the Fraser Valley.

Yes, you are eligible for MCA. As Few college don't required Maths as compulsory subjects for MCA. Like Christ university.

Sri Ram College of Commerce, Delhi. Hindu College, Delhi University. LSR, Delhi University. Hansraj college, Delhi University. Loyola College, Chennai. MCC, University of Madras. KMC, Delhi University. St. Xaviers College, Mumbai. Each College has different criteria available on the colleges web site.