What sort of a plate is the Sunda plate?
Well, in short, it's mainly continental, (oceanic-continental convergence).
But in regards to the &quot;type of plate&quot; that the Sunda plate is, is minor plate or tertiary plate. Meaning it's not very big etc. Because 1 tectonic plate can have both oceanic or continental crust. Tectonic plate and crust are slightly different concepts. So, The Sunda plate is mainly comprised of continental crust. There might be a bit of oceanic crust, but less.
Map of oceanic crust on earth: https://www.ngdc.noaa.gov/mgg/ocean_age/data/2008/ngdc-generated_images/whole_world/2008_age_of_oceans_plates.jpg