Its not clear what you mean by using the word “remotely”.
Are you using iTunes on the local network and simply want to include the WD My Cloud in the iTunes library?
Or do you want to be ouside of your local network at some offsite location (lke at work) and use iTunes to access your WD My Cloud (like at your home)?
From the sounds of it by “remotely” you mean you will be connecting to the WD My Cloud while connected to your local networks within your home/current location. If so one can access their WD My Cloud and its iTunes supported content from within iTunes by selecting the “house” icon (don’t know what Apple calls it) from within iTunes and from the drop down list select your WD My Cloud. The WD My Cloud User Manual if you haven’t read it already explains, generally in Chapter 12 Playing/Streaming Videos, Photos, & Music, how to use iTunes with the WD My Cloud.
One can copy or move their media to the WD My Cloud and configure iTunes so it treats the WD My Cloud as part of its iTunes “library”. There are past threads ( like this one) that exlain how to do it. See the following Apple Support links for more information.
Back up your iTunes library by copying it to an external drive
Move your iTunes Media folder on a Windows PC
If you are trying to access the WD My Cloud while at a remote location that is not connected to your local networks then without the use of a VPN or similar connections into the local network it isn’t possible with the iTunes software alone. As explained in my post above one would have to create some sort connection, like through a VPN, to the local network so one can then allow iTunes to access the WD My Cloud at home. It might be possible to enable FTP on the WD My Cloud and use some sort of app or software on the Macintosh to connect and map that FTP connection as a shared drive so iTunes could then access and use the mapped drive (or FTP connection) as part of its “library”. Do a Google search for “itunes access library remotely” for many discussions on how to accomplish this, possibly using FTP.