Continuing a "stopped" iCloud restore on iOS
iCloud could be slow in restoring especially if you have lots of app data and your WiFi is not Speedy Gonzalez. I have some bad experience restoring with iCloud as my Photos app and Spotify app are both more than 5 GB each. 

There is absolutely no way to let iCloud take over from where it left. You need to do the restore anew. 

I'd suggest, the next time backing up via iTunes or an alternative such as Copytrans Shelbee. The restore will go rather quicker as it is done over USB. The backup in iTunes is exactly the same as with iCloud (including app data).