The 18-year-old tennis player won the boys' junior title at both Wimbledon and the U.S. Open.
Peliwo beat out ski jumper Alexandra Pretorius and wrestler Dorothy Yeats for the honour at the Canadian Sport Awards.
"This is such a great honour to be considered Canada's top junior athlete of the year," said Peliwo, who became the first player in 28 years to reach the junior final at all four Grand Slams. "This award caps an unbelievable season and pushes me even more to improve as I move to the professional circuit."
Peliwo rose to No. 1 on the ITF junior world rankings on July 9 — the first Canadian to do so — and will end 2012 in top spot.
He is also the only Canadian to win two junior Grand Slam singles titles.
Among the other winners on Wednesday:
— Kayaker and Olympic silver medallist Adam van Koeverden was named male athlete of the year
— Gymnast and Olympic gold medallist Rosannagh MacLennan was named female athlete of the year.
— Team of the year honours went to Canada's women's soccer team for their bronze at the Olympics.