I am a well experienced software developer and have developed several AR(augmented reality) applications.
The best way I see this being done is having the cards being sent have a QR code printed on the card with instructions for the recipient to point his/her phone at it, which will open a page were they can download the application that will be used to view the AR invitation using the the card itself as a marker for the AR.
All of which I can build and provide you.
Please message me with any questions,
Thank You