Officially the My Cloud doesn’t sync (through the My Cloud Dashboard) to any online cloud storage service.
Unofficially there are a number of methods to backup a My Cloud to a cloud based storage service. One is to map the My Cloud Shares to the computer then use the cloud based storage apps/software to copy files to the cloud storage service.
Or one can attempt to install Goodsync to their My Cloud via SSH. Note that this method may modify the My Cloud firmware which void’s the My Cloud warranty.