What can I write in an essay using the twenty-first century and Ben Franklin's "Information to Those Who Would Remove to America"?

The most obvious point of departure is a comparison of the circumstances and expectations of people in the twenty-first century who wish to immigrate to America to those of the people to whom Franklin wrote. As Franklin describes it, the people he is addressing are well educated, informed, dignified but lacking in fortune:

that Strangers, possessing Talents in the Belles-Lettres, fine Arts, &c., must be highly esteemed, [and] Strangers of Birth must be greatly respected, and of course easily obtain the best of those Offices [jobs], which will make all their Fortunes;

In contrast, those who immigrate in the twenty-first century are often, though not always, of reduced means, lacking in education and skills, and needing sponsors within American to vouch for their productivity and employment if allowed to immigrate. They have often seen war and famine and dictatorship. They have often experienced suppression and aggression. [This is not always true. Recent immigrants from India and Pakistan are much more like those Frankilin describes, trained as doctors and Certified Public Accounts and professors, than like the ones I describe.]

One point of similarity you might bring out between America then and America now relates to Franklin's description of the academic climate. While there are far more than the "nine colleges" Franklin attests to, there are multitudes of learned people who have studied in colleges and universities and are proficient in "Letters and Mathematical Knowledge" and who "are in Esteem" here.

One thing Franklin sets up as a barrier to immigration is still in effect to some degree in America today, though it has undergone some shift in an opposing direction. Franklin tells people who have "no other Quality to recommend [them] but [their] Birth" that in America we do not "inquire concerning a Stranger, What is he? but, What can he do?" This has been modified to a degree in the twenty-first century in so far as celebrities in film and sports and music etc are given precedence over others both by who they are as well as by what they do.

As you go through other parts of Franklin's essay, look for other similarities and dissimilarities between how things are now and what they were then; considering both things in America and things in the home countries of immigrant groups.

people do not inquire concerning a Stranger, What is he? but, What can he do? If he has any useful Art, he is welcome; and if he exercises it, and behaves well, he will be respected by all that know him; but a mere Man of Quality, who ... wants to live ... by some Office or Salary, will be despis'd and disregarded.