Thanks for your reply Tom. I was only really asking you to explain why a parliamentary system would work better as a multi-party system than a presidential system. I couldn't think of any reason that would be so.I would point out though that another advantage of Parliamentary systems is that they tend to make impossible the sort of deadlocked government that arises frequently these days in the U.S. when Congress and President disagree — for the very simple reason that a Prime Minister loses his office if he loses a vote of confidence in parliament under a Parliamentary system of government.
I get how the parliamentary system would change government leaders more often, or at least a little more often in Canada. I'm not sure that changing government more often is either good or bad.