Sorry to confuse you, the Prime Minister is elected, but he is the one that appoints Senators. The Senators then basically have the job for life, or until they retire. But when you don't actually have to do anything and collect a hefty salary, why bother retiring?
It may only seem like we have a Prime Minister for life right now. The PM is the leader of the party that wins the most seats in Parliment. Over the past ten years, the right wing parties have split into more regional interest parties and have the divided the vote, allowing Jean Chretien's Liberal party to have no real national competition, so they'll stay in power until they do something really stupid to piss off the voters. So Chretien will still be the PM at the age of 70 (which is only a couple years away anyway).
Alright, enough politics lessons...the most important point is that Canada could be on it's way to the most liberal pot laws in the world!!!