ArcGIS doesn't come with datum transformation grid files for Canada. The main NAD27 to NAD83 Canadian grids are available from ESRI Canada or Geomatics Canada. See the Related Information section for contact information.
Provincial grids, including some that convert between ATS77 or NAD83 and NAD83 (CSRS), are also available. Check with regional authorities.
ArcGIS supports the Ntv2_0.gsb and May76v20.gsb grid files. The supported provincial grids, starting with version 8.1.2, are: