I think El-Guest has the correct name for Mr Montague's coffee shop. I've left a punny comment on that answer that has sparked a long and oblique conversation whose significance is not quite clear to many, I'm afraid. I'll explain.
When I saw this puzzle, I didn't find the actual answer, but something else. Mr Montague is, of course, Romeo from Shakespeare's Romeo and Juliet. Romeo is also the letter R in the Nato alphabet. Then I saw the river mouth. Then the cold month. And it clicked: Each line except the last one describes a code word of the Nato alphabet:
Romeo: So speaks Mr. Montague, missing no beat,
Echo: reverberating stutters in tropical heat:
Delta: "Each river mouth's built up, we've got naans to eat;
Hotel: then, lodgings we have; a café would be neat!"
Echo: They're terribly moved by this repeated sound;
Romeo: excited, loud yakking leaves Montague drowned.
Romeo: Like Montague arrived at a truth too profound;
India: entire subcontinents his words astound.
November: Long since then, a cold month; bazaars clear away.
Golf: Boys watch some chess club game with cups of latte.
Sierra: Up high in the mountains, an alluring café,
Oscar: of gold award quality, looms clear as day.
Romeo: "Drink! Savvy old Mr. M achieved his dream!"
Romeo: Earnestly Montague earned his esteem.
Yankee: Excited New Yorkers are hurrying to gleam
some secrets from this man's espresso machine.
This spells out: Red herring. Sorry. And that's what my comment was about: The "seafood" referred to the red herring, that's all. The fact that seafood has a double letter was coincidence.
But there's more:
I don't know how El-Guest found out about the solution. Certainly the double-a words naan and bazaar stand out, so that may have made El-Guest to look for double letters. But the first letters of each line form a reverse acrostic. (I'm sure the "upscale" is meant as a hint to read them from the bottom up.) That acrostic reads: See double letters.
And that's the long route to the café's name.