The difference between trustee and guardian is immense. It is like comparing apples and zebras.
A guardian, in this context, is a person appointed by a court and Judge in a guardianship proceeding to make another person’s (the ward) legal, financial, and healthcare decisions.
The guardian is then responsible for managing the ward’s financial, healthcare, and legal affairs. The guardian is responsible to the Judge in the case. The guardian must report to the Judge annually on the social, emotional, and physical status of the ward. The guardian must also prepare and present an account of the ward’s estate annually. This account is published, typically in a newspaper, and must be approved by the Judge. A guardian may also be required to have a bond (insurance) in order to serve. Guardianship is expensive and can be embarrassing for the ward.
A trustee is the person in charge of managing the assets in a trust for the benefit of the beneficiaries. A trustee has no legal authority to manage the legal, financial, or healthcare affairs for the person who created the trust.
A trust is an agreement between two people for the benefit of a third person. Those two people are the grantor (the person creating the trust and putting property into the trust) and the trustee. The trustee has actual legal ownership of the assets but manages them for the benefit of a third person – the beneficiary.
In summary, a guardian is appointed by a Judge to manage all the ward’s affairs under court supervision. A trustee manages the assets in the trust, but has no control of the affairs of the person.
As you can see the difference between a trustee and guardian is immense and is like comparing oranges to horses. They are completely different and have different purposes.