Hi. I did this:
Initially, I completely deleted EasyAR 2 with the associated plugins from my project to avoid conflicts and imported the new EasyAr 3.0 with just one sample - HelloAR_ImageTarget.
1- I copied the camera, the EasyAR_Setup and the ImageTarget, from the HelloAR_ImageTarget scene and pasted it into my scene.
2 - So I removed the objects inside the new ImageTarget and replaced them with mine - Then I deletes the old ImageTarget from EasyAR 2.3.
3- Then I also changed the image in the ImageTarget / Target Name field and ImageTarget / Target Path by mine in the StreamingAssets.
4- I reconnected the EasyAR_Setup / ARSession / Img Tracker and EasyAR_Setup / ARSession / Camera Background Renderer fields as well as EasyAR_Setup / ImageTracker / Target Camera.
It worked but I still need to adjust the camera because it is showing the 3D object aside ... I will make the final adjustments soon ... I hope this procedure helps you to have a direction to follow.