I also like the new $10 bill, and I would like the switch to polymer bank notes too!
I e-mailed the Bank of Canada about this issue before and this is what my reply was:

In the past few years the Bank of Canada has tested a number of substrates, many of which contain polymer or polymer-based materials, for possible use in the production of bank notes. The Bank continues to be interested in these materials because they could offer both increased security and longer note life, which would result in important savings. There are disadvantages to plastic materials, however. The main one is that the handling characteristics are considerably different than paper. As a result, bank note production is more difficult and there are significant handling problems to overcome once the notes are put into circulation (e.g. compatibility with existing note-handling equipment).

I hope this information helps!