I spent 3-4 hours yesterday trying to do the same thing.
I tried everything but icloud seems problematic.
However, what worked for me is the above:
1) Use ifunbox to access the pvz2 folder in with the savegame.
2) Locate the file com.popcap.ios.PvZ2.plist inside library/preferences and copy it to desktop
3) Paste it to the same direction on the other ios device. If it asks to overwrite, do it.
4) Open pvz2 in both devices simultaneously and wait for a couple of seconds in the main screen.
5) Smile. Your icloud support works.