Masters

Yes, you can do the PG Diploma course after Bachelor of Engineering Electronics and Telecommunication Engineering.

To do MA in Economics, you need to have maths in class 12th and you need to have studied maths in the specified number of semesters which may differ from college to college. If you have done B.Com then you are eligible for MA in Economics but you need to fulfill the criteria of studying maths.

The expected cut off for M.Sc Maths PG is 85%.
That means you have to have a score of 65/75.
It will be quite tough for you to take admissions.

To get admission in a good university in the US, you should have a good score in TOEFL and your Bachelor's degree without any backlogs or supplementary exams.

You have not specified the college you are seeking admission to. But I see that you have a Diploma. Unfortunately, Diploma is not considered as a graduation course. The minimum requirement for applying to MBA is, the candidate must have completed his/her Bachelor's degree with 50% of marks from a recognised university.

Best universities for MS in Computer Science in Canada:
University of British Columbia (UBC): The UBC Department of Computer Science, established in May 1968, is one of the top computer science departments in North America.
University of Waterloo
University of Toronto
McGill University
McMaster University
Queen's University.

Miranda House doesn't offer PG courses.
But you can definitely apply for PG in Faculty of Sciences, Delhi University.

Just go ahead and fill up the forms of the college. If you have got a good score then you can definitely get admission. All the best.

Hi! Check this link to know top colleges for Master's degree in Economics by comparing there ratings and other important details:
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/humanities-social-sciences/economics/colleges/m-a-colleges-india&ved=2ahUKEwiP4aKom6XjAhUh7HMBHRHfAoYQFjAGegQIBRAB&usg=AOvVaw28Jwu0ysEswRRX9VSADZo4.