Yes, you can name a guardian in your Pour-Over Will if you have minor children – this should be someone you trust to have custody in case something happens. The guardian has physical control over the minor children, including the responsibility to provide for their physical care, health care, education, and general welfare.
The responsibilities of the guardian do not include control of finances for the children. If your planning includes a children's trust, your trustee will have the responsibility to invest the assets of the trust and make payments to the guardian for the care of your children. If you want, you can choose the same person(s) to be the guardian and trustee.