To be very frank, I don’t think, all the three parameters stated by you, i.e. (1) strong resume, (2) US certification in HR, and (3) Volunteering work, will have great weightage in grabing the HR job, selection of which will be on talent/intellectual levels.
The abovestated three points make excellent addition to your personality, which ofcourse anybody will appreciate largely, when you appear before an interviewing officer.
I do not know much about ‘HR course in US’, but knowledge related issues, in India, like, labour laws, factory act, shops & establishment act, PF / ESIC matters, and many such subjects, which HR is suppose to be well aware, I think are totally different than US studies.
I hope, since you have still time to come back to India, you may start preparing yourself, looking at the Indian rules, regulations and various aspects, so that when you get an opportunity to work as HR, you will be very comfortable and successful.
Comments by Mr Simhan, Super Moderator, are very much valid and carries good meanings. My personal thanks to him.