I\'m just playing around with AR core and want to have an object flying around the room and able to land. I\'m unsure about how to add colliders to the planes that ARcore is
Assuming you are doing this in Unity, you may want to use a Mesh Collider on the surface instead of a Box Collider.
I'm not sure about ARCore in Unity specifically, but in other AR frameworks it works something like in the attached screen shot, so I imagine it would be similar.