CRA has provided some comments on registered charities and political activities.
We have consolidated these various articles into one document.
CRA information on registered charities and political activities.pdf
[Update – CRA has created a new space on their website with more detailed information on political activities at: http://www.cra-arc.gc.ca/chrts-gvng/chrts/cmmnctn/pltcl-ctvts/menu-eng.html]