I'm not convinced that e-commerce sites even CAN be a "content farm". They can, however, be a kind of database spam. However, the situation you describe doesn't sound that way to me. In fact, if "manufacturer" and "type" are different for the different URLs, then each product is clearly different and I don't see how a canonical link makes any sense. Within a given manufacturer and type, you might consider a canonical link for minor product variations like color.