There isn't a DVFR type flight plan any more. ICAO doesn't provide for them. The FAA Domestic flight plan form used to have a DVFR check box, but there isn't an equivalent on the ICAO form, so filing a VFR flight plan with "DVFR" in the remarks will work. Even if you don't include "DVFR" in the remarks, any VFR flight plan that penetrates an ADIZ is treated by Leidos (aka FSS in CONUS) as a DVFR flight plan. The AIM and FAR part 99 describe what is required in the flight plan, how to activate and close it and all other requirements. You need to establish radio contact with ATC or FSS prior to entering the ADIZ and if you have not already been assigned a transponder code, you will get one assigned. FSS can assign a transponder code when you file the flight plan and you should squawk that code unless ATC assigns you a different code, which then overrides the FSS assigned code. Leidos only supports filing a flight plan departing from one the following countries: US and its territories, Canada, Mexico, Bahamas, Turk and Caicos.