Q. Can a writing team that's half Canadian / half American qualify for all the Canadian goodies?
A. Sorry, no.
Ah, I found the answer via this CPTC PDF: http://www.pch.gc.ca/DAMAssetPub/DAM-flmVid-flmVid/STAGING/texte-text/cptc_guide_1272631234182_eng.pdf
To obtain the points for the position of screenwriter, a production must meet one of the following conditions:
a) Each individual involved in the preparation of the screenplay for the production must be Canadian. This means that all the individuals engaged in developing the screenplay, from the outline or treatment through the various drafts and dialogue polishes to the final shooting script, must be Canadian; or
b) The principal screenwriter must be Canadian and the screenplay for the production must be based on a work authored by a Canadian and published in Canada.