For the kindle, yes, get the kindle app and then you can sync your books to the iPad. Also it will remember how far you've read so easy to switch between devices. Don't know if something similar is available for the Sony.
If memory serves, Sony uses the ePub format. There are several apps that can read ePub books that are not DRM (copyright protected). iBooks and Stanza are two that I have.
As far as I know, Sony does not have an eReader app for the iPad.
