Re: My pvz2 app cant open and i am not sure if i had backed up my progress.

If worrying about your progress, I suggest try to try the following 2 options first before carrying out any re-installation.

1.  Note down your player ID.

On IOS you can get this information without starting up the PVZ2 App.  It is located under

Settings > PvZ2 > PlayerID 

I am not familiar with Android so not sure if this information is available without starting up the PVZ2 App, if your App is not starting then there is little you can do except trying option 2 below

2.  Turning off internet data and WiFi, try to see if the App starts up on 'local' mode.  if this does get you to the main menu screen,enter to the game mode selection menu and then re-enable WiFi (internet). Exit back to main menu screen and click the Cloud button to register your email (and get 100 free gems) if you have not done so before.  This links your PVZ2 account (and your progress) to your email and allow you to recover it on subsequent PVZ2 installs (even cross platform to another device).