Detailed instructions for doing this are here: http://www.ifixit.com/Guide/Mac/MacBook-Pro/SuperDrive/85/6 however this will void your warranty if you are not an apple certified technician.
If you're referring to the MacBook Pro's optical drive, those made mid-2012 or earlier and are non-Retina reside hidden either in the front or the side. MacBook Pro Retina versions don't have an optical drive.
Unfortunately, the MacBook Pro Retina is too thin to support any current standard of hard drive.
The MacBook Pro has more upgradeable items like the hard drive and Ram that you can replace yourself and the MacAir has the Ram and hard drive (flash drive, SSD, etc) soldered directly to the main board so you can't up grade them later. The MacBook Pro is a bit more powerful then the Air but the Air is much slimmer and lighter then the MB Pro.
The $1,199 13" Macbook Pro comes with a 500 GB hard drive. The $1,499 13" Macbook Pro come with a 750 GB hard drive. The 15" models come with the same amount.
Your CD/DVD player is a Read Only Memory drive.
Any standard USB Flash/Thumb drive will work with the MacBook Pro. The "best" will depend upon the specific needs of the individual user.
Most do, but the Macbook pro with Retina Display does not.
The hard drive should install and format just fine. However, if you're looking to use the pre-installed Mac OS X and software from the newer MacBook Pro on the older MacBook, it probably won't work well, if at all.
MacBook Pro is the best you can get
macbook pro with retina display way better
If you mean, would you be able to access Google Drive on a MacBook, yes, you can do that. Google Drive is accessible across nearly all platforms, and you can upload and download from it, read and edit from it freely on a MacBook.
The macbook pro!