when Surface is created, there is a buffer associated with it, which is used to hold all canvas data related to this surface. And there could be multiple surafce created at a time in android application.
So my doubt it, as there is limited number of framebuffer like 3, how each surface's data is mapped to to final framebuffer which will be updated ?
The notion of "framebuffer" is becoming antiquated. Individual surfaces are composited together, but there may not be an actual framebuffer that receives the data. See, for example, the various ways to composite the screen noted in this answer.