Backblaze will backup iCloud and Dropbox:
iCloud does not have a dedicated folder like DropBox and Google Drive. The iCloud Drive files are located at /Mac HD/Users/<your username>/Library/Mobile Documents/
Backblaze can also backup your Dropbox folder.
One thing to keep in mind is that Backblaze cannot upload files if they are exclusively locked by other programs. Since Dropbox items are often frequently open, you will want to make to periodically close out of all of your programs.