LINQ из нескольких таблиц
from p in Product
from c in Catalog
from m in Manufacturer
where c.Id == p.CatalogId && m.Id == p.ManufacturerId && p.Active == 1
select new
{
p.Name,
p.CatalogId,
p.ManufacturerId,
c.Name,
m.Name
};
Code with bulbul