I have come across this sentence:
Kashmir is regarded to be the heaven on earth.
Is there a difference between that and
Kashmir is regarded as the heaven on earth.
"Regarded to be" sounds a bit odd to a native speaker. There is a hint of unnecessary repetition which would not be there with a different verb as in "...is thought to be...". 'Regarded as...' would be preferred.
"Heaven on earth" is a stock (adjectival) phrase; it does not need the definite article.