Upload specific Photo photos to Google Drive
Not having Goole Drive I am making an assumption here that you have a folder of some sort that you can drag files into and out of, similar to Dropbox.

If you select the photos in Photos.app that you want exported to Google Drive and then tap ShiftCommandE that will prompt you for the kind, size and quality of the picture. Once selected click Export and point the file dialog box to your Google drive folder.

Note that Photos.app will remember the kinds, size and quality settings from the last export so you will likely only have to select those options once.