Kindly let me know if Indians working in USA for last 3 years need to go through the English language assesment test for the Canadian application ?
Thanks for your help !!

I don't think working in the USA gives or takes anything away from your English language skills.
Basically, you have two choices for your points -
1. Give the test and get the guranteed number of points based on your marks.
2. Provide evidence in lieu of the test and depend on the officer to give you the points you want.

I don't think that the fact of working in the US will give you full points for language.
You will have to provide other documentation and evidence.
See:
http://www.cic.gc.ca/english/skilled/qual-3-2.html

If you choose to do so, make sure you read the entire contents of the 200 page Manual of Canadian Language Benchmarks at
http://www.language.ca/pdfs/clb_adults.pdf

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