Most likely in the US I think it's just going to take more states to legalise it recreationaly. Once enough states reach that point then the Federal Government will give in. No idea how long that will take. Perhaps legalisation in Canada will influence the US to do the same more quickly.
There's going to be demand for legally taking weed across the border at some point. If it's legal in Canada and legal in Washington then shouldn't people be able to legally transport it across the border like you can with alcohol? That will likely become an issue at some point. Doubt anything will be done about that for a while though. Right now if you cross the border and they ask you about your drug history you have to say you've never smoked weed ever in your life otherwise they can prevent you from crossing the border (even when travelling into Washington where it's legal).