Getting back to the "riding" question from earlier, Canadian ridings don't have to correspond to counties/cites, etc., although sometimes they do. After every census (every ten years) an electoral boundaries commission examines the existing ridings and readjusts them to conform to population shifts, etc. There would appear to be scope for gerrymandering in this, but the commission is supposed to be independent of the parties and the government. I don't ever remember any scandals over redistribution.
There are 301 ridings for 22 million people, so each riding represents an average of 73,000 people. Rural ridings tend to have fewer people and urban ridings more, with defined upper and lower limits. The Yukon and Nunavut have one member each by law, even though their populations are lower than the minimum.