If the FK is nullable, the join will be a left join. If the FK isn't nullable, it will be an inner join. This is the only way it's determinable what you want as Linq lacks any other system to specify the join type in this. Your link must use a nullable (optional) FK side as well to get a left join.
If nothing helps, please use queryspec, the query api will allow you to specify the join type in any case.
ps: please next time post on our forums, we don't monitor SO every day, but we do monitor our forums.