In order to write a convincing persuasive essay on how an accent can limit a person's chances in life, you need to appeal to both logic and emotion while using reputable sources. I also believe you may have to focus your topic to concentrate on accents from, at most, three different countries. These might become your focus.
You would appeal to logic by doing research to discover the "big-picture" background on the effect of accents on life opportunities, such as in getting a first job and getting promoted. Look up some studies on careers and accents to see what they have to say. What are the broad statistics on someone getting held back by having an accent? Are certain accents less desirable than others? Why? One could hypothesize that a person with an accent from a country that is associated with negative stereotypes in the country they are now residing might have a harder time succeeding than a person from a country with positive stereotypes. I would start Googling topics such as national accents and job success and see what came up.
Second, to be convincing, a paper has to be emotionally moving. The classic way to appeal to a reader's emotions is through the story of a single individual. You would do well to find an article about a person held back because of his or her accent despite having good credentials for a job. One such compelling story is good; two or three are optimal.
Finally, as you do your research, be sure you are using credible sources. These would include journals and newspapers that are recognized for quality, such as the New Yorker, the Atlantic, the New York Times, or the Washington Post. Scholarly articles are also golden: look for those with .edu at the end, and if you are in doubt, google the author or authors to check their credentials. Do not go to their own websites to research their credibility, but do try to find out what others have said about them.
If you carefully research your topic using reputable sources, include facts and statistics to give an overview of the effect of accent on life success, and include several personal stories, your paper is almost certain to be effective.