Highlight all the photos in the google photos app by highlighting one and dragging your finger to the right and down. Then tap the share button and choose copy. Do about 500 at a time, then switch on wifi so the photos upload to photo stream. Then from iphoto on a mac, take the photos in photostream and add them to a new icloud album. I believe there's a 10,000 photo limit but no size limit. Then delete the photos from photostream and do the process again until all photos are shared to your new icloud album.