Saw this story just now at the Globe and Mail. Long and short of it, the Liberals have basically endorsed the idea of legalizing marijuana and are moving the discussion in their party to the complexities of implementation.
Even if the Liberals are the third party in Canadian politics after the last federal election, my understanding is that they are the centrist party with lots of connections and support in the business community. One of the biggest obstacles will be the various anti-trafficking treaties Canada has signed over the years. The path from a third party's platform to federal policy is a long one, but Official Opposition, the New Democrats, have already adopted this position. The only major party that remains opposed to the idea are the Conservatives. Since they can hold on to power for the next four years or so, no movement can be expected soon. But they won't get elected into perpetuity and as soon as they are defeated Canada is guaranteed to have a governing party or coalition pledged to marijuana legalization.