It appears that the decision to go polymer came long before good quality fakes of the Journey $20 to $100 notes started to appear. BOC experimented with polymer substrates (Luminus) before Journey notes were introduced. I think what prompted the move was rampant counterfeting of the Birds notes (the notes in the Hyunday must have been Birds twenties) and the new $5 and $10 notes in the Journey series that proved to be a major flop. I remember getting 4 fake tens in change in 18 months in 2003-2004, which means as many as 1 in roughly 200 tens in Toronto could have been counterfeited. Almost each small grocery store I went to had several of these fakes pinned to a wall. The 730 ppm surge in counterfeits at that time could easily be attributed to the Journey tens alone. It's interesting that the article does not mention this.
In my opinion, the upgraded $5 and $10 Journey notes as well as the original Journey $20, $50, and $100 notes have decent security features. The hologram and the watermark could be duplicated, but the security thread is much harder to copy.
In any case, the polymer notes bring banknote security to a new dimension and are certainly a welcome change. As the article says the polymer substrate itself is the most important security feature.