Here's some info. The cost last I heard was around 2500USD. Here's the website to find more info including printing options to get the paperwork started.
Staff Instruction (SI) No. 401-001
6.2 Commercial Pilot – Aeroplane
To convert an FAA commercial pilot or Airline Transport Pilot certificate to a Canadian Commercial Pilot Licence, the applicant:
Must hold an FAA Commercial Pilot or Airline Transport Pilot Certificate – Airplane Single Engine Land or Airplane Multiengine Land, as appropriate for the rating sought and not endorsed “Issued on the basis…” of another foreign licence.
Must provide proof of a minimum of 200 hours flight time in aeroplanes.
Must pass the FAACA – Examination, Commercial Pilot Licence (Aeroplane);
When the holder of an FAA Commercial Pilot Certificate does not hold an Instrument Rating, the US certificate bears the limitation "Carrying passengers in airplanes for hire is prohibited at night and on cross-country flights of more than 50 nautical miles". This licence notation imposes an operational limitation on US commercial pilots without an instrument rating that is similar to the one imposed by CAR 703.88(3). Holders of commercial pilot certificates with this limitation have completed all commercial pilot certificate requirements. When all other aspects of this conversion process have been met, we should issue an unrestricted Canadian Commercial Pilot Licence.