Yes, candidates who are existing work pass holders or who are currently overseas are able to apply.
You should only have your work pass cancelled after your Overseas Networks and Expertise Pass application is approved and when you are ready to get the pass issued. Do note that once your work pass is cancelled, you are not permitted to work until you get your Overseas Networks and Expertise Pass issued
For current Employment Pass (EP) holders, you should ask your current employer to
cancel your EP.