I finished my deferred sentence 3 years ago and my case was dismessed, I am now applying for a new job and was wondering to I have to answer yes to pleading guilty for a felony or can I answer no. Can they even find that I had a deferred sentence when they do a background check. Thanks for the help.

What does the question say, I have never seen a question have you plead guilty to a felony. Normally they ask have you been convicted of a felony.
And in your case since it was dismissed, no you have not.