Learn Portuguese (Portugal): Este prato é conhecido em todo o país.

In Portuguese, including the definite article changes the meaning of todo. Todo o país means 'the whole country' or 'all of the country'. If you drop the article and say todo país, it changes the meaning to 'every country'.

Why use é instead of está for conhecido?

We use ser (é) rather than estar because this is a general, permanent fact about the dish, not a temporary condition. It forms a standard passive voice construction indicating that the dish is known by people in general.

Could I say por todo o país instead of em todo o país here?

Yes, both are perfectly natural! Em todo o país translates literally to 'in the whole country'. Using por todo o país is like saying 'throughout the whole country', which adds a slight feeling of the fame being spread or scattered everywhere.

Is país pronounced the same as the word for parents (pais)?

No, the accent mark makes a big difference here. País (country) is pronounced with two syllables, stressing the accented í. The word for parents, pais, has no accent mark and is pronounced as a single syllable.