Fake polymer notes are now entering the market. Short article from the National Post can be found here, where they show what you can look for on a genuine note:
http://news.nationalpost.com/2013/05/16/rcmp-worries-canadians-are-overconfident-in-new-bank-notes-as-police-find-multiple-counterfeit-100-polymer-bills/
Hopefully none of you have been lucky enough to receive one of these yet!
-TT