N7 Google Book Format?

I don't think you can sideload books into Google Books. I do a lot of reading on my N7 and personally use Mantano Reader or Aldiko which are both fine readers and handle most formats (not Kindle) with epub being preferred. You may wish to try out one of those or any of the numerous others.

 

After connecting the N7 to my PC, I created a folder called Books and placed my files there. Most of my eBooks are in the .mobi format, so it took a little trial and error but I tried and love the free Cool Reader app.

I am hopeful one day Google Drive will be enhanced to allow my eBooks to be opened from there. It allows a file to be "pinned" or stored locally on a mobile device, but you can't choose the location and I've been unable to get an eReader to access them that way.