For me, stunners are women who are unusually exciting, to such a degree that a single glance can destroy all semblance of logical functioning in my brain, make me forget what I was doing, and overwhelm me with desire. Most often, such women would fall into the category you might call buxom - full-figured, curvy and utterly sexual women. Women overflowing with a femininity and sexuality so powerful it threatens to overtake and envelop you so completely you'd make some rather poor life decisions
examples-
Angel Lola Luv
Christina Hendricks, especially from her pre-Mad men times, like in Firefly
Scarlett
For whatever reason, I rarely see Japanese "stunners" as they tend to have a more elegant or cute look rather than undeniably sexy look. Thats fine, and still attractive, however it doesn't fit the "stunner" label IMO. However, there is one in the movie Shinjuku Swan who is incredible. Don't know her name though! The video here is set to start where she comes in: