It will be legalize, not decriminalize. The party has majority, they could have passed a decrim on day one. They have no intent of decriminalizing.
Legalization on the other hand, which is what the current gov is going for, is legalization. And that requires all those special departments, policies, procedures, laws, etc...
See for example:
http://www.economist.com/blogs/economist-explains/2014/06/ec...
versus
http://globalnews.ca/news/2650706/canada-to-introduce-pot-le...
The globalnews article talks a bit about how the Liberals tried decriminalizing it in the past and failed. And Justin Trudeau saying why they won't decriminalize before they legalize it. But the focus is on the legalization/regulation of it next year. It is not using those two interchangeably.