What is the difference in guardianship and power of attorney?

To add to previous responses, POAs can vary, depending on how they are structured. Some are effective immediately. Some are "springing," i.e. based on a future event like incapacity/dementia. Some POAs are structured to require a doctor's verification of lack of capacity to be effective. It depends on wishes of the principal. POAs are often one part of a more comprehensive estate plan. Guardianships (conservatorships) are obtained through court proceedings.

BIG difference. A Guardian carries a court order signed by a Judge and only the judge can revoke it. A POA can be granted and revoked by the parent five minutes later and granted to someone else.

You only get guardianship if your parent can't make their own decisions. Like dementia. POA is for the future. Like if your parent has to go to hospital and temporarily can't make their own decisions. Or you need to take over their banking because it's too much for them.