How to get the virtual camera to keep object in view?

Consider attaching a CinemachineTargetGroup to your Virtual Camera. This allows you to frame multiple objects at once. With this you can place some small objects (perhaps non-rendering) at the edges of your large object and always keep the entire object in view.

 

Yes, that's a very good idea.

To clarify: create a new GameObject and add the CinemachineTragetGroup behaviour to it. Add your target object and the extra (perhaps non-rendering) objects to the target group. Then, use that target group as a look-at target for your vcam, and set the vcams' Aim to Group Composer. That will expose some settings that let you control how the group is kept in frame. Or, if it's a 2D vcam with a Framing Transposer, it will auto-detect the group and you can leave Aim on the Do Nothing setting.