SELECT DISTINCT T1.type FROM mill AS T1 JOIN architect AS t2 ON T1.architect_id  =  T2.id WHERE T2.nationality  =  'American' OR T2.nationality  =  'Canadian'
What are the distinct types of mills that are built by American or Canadian architects?
[Schema (values) (types)]: | architecture |  architect : id (text) , name (text) , nationality (text) , gender (text) | bridge : architect_id (text) , id (text) , name (text) , location (text) , length_meters (text) , length_feet (number) | mill : architect_id (text) , id (text) , location (text) , name (text) , type (text) , built_year (number) , notes (number);