How do I attach buttons to object (3d plane) ?

I am using unity arkit and want to add 3 buttons to a 3d plane. I want the buttons to be anchored below the card so when pressed, video plays on the whole of the card. I tried to attach the buttons and canvas to the plane but when I build the buttons are either fixed to the screen or just in mid space. any suggestions would be greatful.

This is for an AR app.