Canto allows admin-level users to define the mapping of IPTC/XMP/EXIF metadata information from a file to the Custom Field of their choice in Canto.
To enable this feature go to Settings > Configuration Options > Custom Fields > Metadata Mapping
You will enter the IPTC/XMP/EXIF metadata field name from the file on the left. While on the right, you would enter the name of the Custom Field from your Canto instance you want the two fields to map. Click Add, and you're all set!
Note: The Custom Metadata Mapping feature only maps to Custom Fields and no other fields in your Canto instance.