Here I think I share some of the concerns of Mr. Loewen.
Proportional rule has worked very well in many countries around the world. However, for Canada, it would represent a very substantial departure, a much bigger departure, from the current system than majoritarian systems, such as alternative voting and majority rule.
In particular, proportional rule would presumably eliminate the current system of single-member electoral districts. Canadians are used to the idea that in their district they will be electing an MP. That would change under proportional rule. Also, there is the idea that a majority government could well go by the wayside. Many countries using proportional rule today patch together coalitions to form governments. That's a much more likely outcome under proportional rule than under a majoritarian scheme.
My own philosophy in these matters is to make reforms when there are clear directions of improvement, but not to take a bigger step than is necessary to accomplish an improvement.