I do have a 3 year degree in B.Sc (Computer science) am i eligible to apply for MS (Computer science) in USA or Canada?
This is indeed an issue as most universities insist on a 4 year undergraduate degree from India to be eligible for a masters degree admission. The other alternative they provide is you having finished a 3 year undergraduate degree + a 2 year masters degree in India before you apply for a masters in a Canadian university.
Having said that, it is program specific and you will have to contact them in order to check if they would accept your degree without the additional 2 years of MSc with it.
A friend of mine has the same issue right now. He is doing a 3 year undergraduate course in Political Science. He had contacted many universities to check on this rule with them, and except a few such as Queens, UBC, Carleton and McGill the others said they will not accept a 3 year degree for admission.
BUT depending on the course, they might make exceptions for a 3 year BSc degree from India as long as your institution has an, otherwise it would not be possible.
You are, however, strongly recommended to contact the graduate department of the universities you are applying to, in order to get a better idea