https://portableapps.com/apps/utilities/dsynchronize_portable
http://www.dirsyncpro.org/index.html
https://www.microsoft.com/en-us/download/details.aspx?id=15155
One of these should do the trick, although I don't think SyncToy support real time sync.
It's pretty simple, just use the following command from a command prompt with admin privileges:
~~mklink /j "c:\users\<accountname>\Google Drive\<Save folder name>" c:\users<accountname>\appdata\roaming\darksoulsiii~~
EDIT: It seems like the symlink file is updated but google drive is not syncing the update. I'm looking to see if there is a way to get it to sync so it's properly backed up.
EDIT 2:Well it does not seem that Google Drive, DropBox or OneDrive will back up a symlink based solely on file date (I haven't tried MEGAsync yet). However, you can use DirSync Pro (http://www.dirsyncpro.org/) and set up a copy job that uses the real time scanning to copy the files when changes are detected. GoogleDrive will sync these changes and you get the added benefit of version control (http://imgur.com/SpxsjBB) so you'll be safe if a hacker gets to your latest save.
And that should be it. The only downside i see is that there's no version control (at least I don't think there is, i haven't looked into it) so if you were hacked and the game saved it would backup that new save.