Dec. 27/13-A Bombardier CL-600-2B19 (C-FEJA) operated by Jazz Aviation, was departing Saskatoon (CYXE) when the crew observed the nose gear did not lock up and a gear disagree warning illuminated. The crew climbed to a safe altitude and conducted emergency checklist procedures. The crew could not obtain a nose gear up and locked indication, but did achieve a landing gear down and locked indication. The aircraft was overweight for landing at Saskatoon, so the flight diverted to Calgary (CYYC) with the gear down. The crew declared an emergency, and the flight landed at Calgary without further incident. Company maintenance removed and replaced the nose landing gear.