When you migrate photos from Picasa/Google Photos to Flickr using PicBackMan, the EXIF data (associated with small images) is retained. As far as bigger photos are concerned only the name is retained.
We tried doing this at our end and found that photos upto or less than 10MB retained their EXIF data. However, images bigger than 10 MB could not.
PicBackMan is a free photo/video uploader that helps you to keep your memories backed up to your favorite online services.
Users in 130+ countries have backed up.
... an excellent job of uploading more then 300GB of photos to 2 different services