You can find vintage plaster molds for sale online to compare values. Remember that molds signed by a known artist are more valuable than new, or old unsigned pieces. As Emanuel Hahn is a known Canadian artist, his pieces will command more than others. Hahn was a member of the Royal Canadian Academy of the Arts who helped design memorial monuments in Toronto, Ontario, and Ottawa. He headed the Ontario College of Art's sculpture department during the first half of the 20th century.
Be careful when handling an old plaster mold. Do not clean but for a light brushing if you must. Do not clean with water. Pencil marks should be left as they are an intrinsic element of the piece.
For more information, clues, or suggestions on how to proceed with your research, contact your state arts council. My state, for instance, even hosts an art marketplace online.