otixo + webdav
you can try otixo.
otixo can connect to multiple cloud services in the backend and expose the unified view using webdav.
there is a webdav client on Linux(I think it is written in fuse), which will let you mount webdev shares/locations and provides access using posix calls.
Not sure if webdav client(and the protocol) support NFS/CIFS like granular ops over the wire, but it does expose data through posix apis.