Canyons and stuff

Question

This turned out pretty easy, but enjoy anyway.

The grandest of canyons is found within me;
few can match my nature's diversity.

The continent's largest metropolis I boast,
along with a long stretch of Pacific coast.

Beside me a massive saltwater gulf lies
and I possess some Caribbean isles.

I think that these clues are sufficient, mates.
Tell me the name of these united states?

Looking for the name of a country.

Answer 1

I think the answer is:

United Mexican States

The grandest of canyons is found within me;

I think we are talking about the Copper Canyon

few can match my nature's diversity.

The nature of Mexico is very diverse

The continent's largest metropolis I boast,

Mexico city is the largest metropolis in North America

along with a long stretch of Pacific coast.

Beside me a massive saltwater gulf lies and I possess some Caribbean isles.

And it matches all the above due to its location

And, of course, all the above might probably apply to:

the USA but then it would have been too simple