Help Transferring Characters from Xbox 360 PvZ Garden Warfare to PvZ GW2 Xbox 1

Good afternoon.  I need assistance with transferring characters from Plants vs. Zombies Garden Warfare for XBOX 360 which is saved on a Storage Device and is too large to save to the XBox Cloud Saved Games service.  I bought an XBox One for my son as well as the CD game for Plants vs Zombies Garden Warfare 2 and he was told and there are YouTube videos by gamers showing that the PvZ Garden Warfare characters from the XBox 360 game can be transferred/imported to the PvZ GW2 game by going to the mailbox behind the house.  When we go to the mailbox on the PvZ GW2 game, it does not give us the option to import or transfer the characters.  We have the storage device plugged into the XBox One.  

The PvZ Garden Warfare XBox 360 game is on our storage device and it is 2.5gb and our XBox Cloud Saved Games storage limit is 2gb, so I cannot save to the XBox Cloud.

I need any help anyone can provide how I can transfer the PvZ Garden Warfare xBox 360 characters saved on our Storage Device to the PvZ GW2 XBox One game.  This would make my son's day (and mine) if anyone could help me figured this out and make it happen for him.  He worked really hard to get all of the plants and zombie characters and this would be awesome if he can transfer them and use them on his PvZ GW2 XBox One game.

Thank you!