What is the average growth rate of the Katsura tree (Cercidiphyllum japonicum) in Southern Ontario?
It will be well-watered in a sunny North facing front lawn.
A Katsura tree is a lovely medium-size specimen tree. Your front lawn sounds like a good location for it in the sun.
There is a variety of estimates for the growth rate of the Katsura, in Ontario but most experts seem to assess it as a reasonably fast growing tree which may take several years to reach a height of 40 feet. The growth rate can depend on the location, soil, climate zone and watering practices.
The following website has good basic information on Cercidiphyllum japonicum, and also several interesting and positive comments sent in by various home-owners which include observations on the growth process of their own katsuras.
A good reference book for all basic information about this tree is the following;
Dirr, Michael Manual of Woody Landscape Plants; their identification, ornamental characteristics, culture, propagation and uses c. 1983
Enjoy watching your tree mature over the years.