In theory you should be able to pursue such a career. However, in practice it is probably not likely even with a full pardon. Once you are sure the record has been properly sealed, I would consult with an employment law attorney to guide you through the application process. Best of luck!
Yes, that is the purpose behind sealing that you can safely raise your head high and say legally there is nothing outstanding against you. There are couple of exceptions, first it is child molestation. Some other agencies like FBI can always open the record including CIA. However, law enforcement is a very wide area. If you mean police and other higher agencies, perhaps they can open it, but not regular security agencies.
Only see a licensed attorney before you make any decision. This answer may not be perfect in any given situation. However, more fact may be required by your local attorney.
Since these records are likely open to the Police and you have no Pardon I think your chances are very poor.
My offices does represent people from Avvo if they contact me but only in the Los Angeles, Orange, Ventura, San Bernardino and Riverside County in Southern California. The answers I give here are not meant to create an attorney client relationship. When accepting clients I conduct interviews face to face and they often take 30 minutes or more. I approach trials and issues from a legal and common sense approach, This is how the majority of judges I have appeared before in 40 years also make decisions. I do not intend by my advice to enter an attorney client relationship and in most cases advise to obtain legal representation. Sometimes if you can not afford it a consultation or limited scope representation is available. As an experienced attorney I can tell you, judges can be impatient, hate emotional arguments and over exagerations or lies. A brief outline of the problems and desired solutions is often best and I d0 limited scope representations advise clients on how to proceed at time of hearing or trial and my fees are considerably less when I do not appear in court as it takes much less of my time.