The senate is a complete mess.

As for ridings, they try to limit it to something like 125000 (I'm not sure exactly). However, it's by the census and some areas in the suburbs near big cities grow so rapidly, 5 years or however often the census is can be a lot, especially depending on when the election is as well.
In some of the small unpopulated areas, it is because of old deals where they cannot lose ridings (East Coast Mostly). In others, it is the very underpopulated and large northern regions. Actually when looking at a national map of the colours won, sometimes it is completely misleading because there are some ridings that are 500000~ 1 million square kilometres (the three territories and the northern ridings of the larger provinces. Then there are the ones in the city that are like 20 square kilometres if that.