WITH A CAREFUL HAND, Donald Akenson has written a piece of witty and entertaining historical speculation. The subject of At Face Value: The Life and Times of Eliza McCormack/John White (McGill-Queen`s, 245 pages, $24.95 cloth) is one Eliza McCormack, a supposedly female transvestite-prostitute who, through intelligence and good luck, lived as the Canadian Tory MP backbencher John White in the late 19th century. What is genuinely convincing here, despite little concrete evidence about his subject`s true life, is Akenson`s portrayal of McCormack-Whites childhood in rural Ireland and what she came to in 19th-century Ontario -a hard, uncertain life, with church politics as the foundation for survival. Akenson provides cameo appearances by the Orangeman Ogle Gowan (the subject of his last book), Susanna Moodie and her husband Dunbar, and Reverend Egerton Ryerson, who visits White in her Elizaprostitute stage, but only for the sake of an odd emotional outpouring, not sex. In the end, At Face Value does not prove that Eliza McCormack/John White was the first woman in Canada`s parliament (Agnes Campbell MacPhail still holds that record, officially). But then I hope that wasn`t Akenson`s intention. As he says early on in the book, in referring to a Daniel Defoe piece about cross-dressing female pirates that inspired Eliza,"the volume was not history but an evocation of possibility`