CanWest is a publishing/broadcasting company and thus falls under similar Canadian ownership rules.
Look at the Beer Store in Ontario. It is owned 49% by Labatt (Belgian), 49% by Molson Coors (American) and 2% by Sleeman (Japanese). It is now wholly foreign owned, but still allowed to operate in Canada.
George Gillet, though an American, was allowed to own 80% of the Montreal Canadians and the Bell Centre.
Target just recently bought Zellers from HBC, which is itself owned by Americans. If the rules are the same, why can Target operate here but Verizon cannot?
Though their may be different guidelines on how to operate in Canada, clearly foreign ownership is allowed in other industries.