Developers can use Apple’s iCloud APIs to sync app data between different versions of their app on Mac OS X and iOS.
If a developer has a Windows version of their app, c
iCloud is available for Windows, yes.
The downloads are available from https://developer.apple.com/icloud/downloads/
I haven't found documentation explicit for Windows yet, though. Your best bet is to do a scan on Apple's "private" dev forums" and do a keyword search on "iCloud" & "Windows" and you'll see plenty of chatter asking the same question as you.