Alice Mary Cadeau was born in Burlington, Ontario, the youngest child and only daughter of an once-aspiring actress from Hamilton and the French-Canadian from Penetanguishene. Her father died when she was 6 years old. She attended Stoneleigh-Prospect Hill School for girls in Greenfield, Massachusetts; Edenhall Convent of the Sacred Heart in Philadelphia; and Havergal College in Toronto. Cadeau appeared as Elizabeth Rex at age 10 with the Hamilton Players Guild, and when 13 in Terrence Rattigan's Five Finger Exercise. She studied under Dora Mavor Moore.