Cross platform progress transfer has been available for years and the process is quite simple.
1. On your old device (Android), register your email address with the App (and receive a small amount of gems rewards if this is done the first time) so your progress is linked to the email address.
2. On the new deice (iPhone), install the game and perfrom the same email register using the same address, you will be given a code to your mail box to verify you are the owner of the PVZ2 account, once verification is complete, you will see an ID conflict message on the screen and be given a choice to load your progress onto the new device. Please ensure to sellect the old account with your original progress, this is important, because if you do decide to start a fresh game from this point, your old progress will be overwritten!