Starting your cover letter with “Dear Editors” or, for example, “Dear North Dakota Quarterly Team” are both acceptable options, but why not take a minute and find the names of the people you’re submitting to? You’re trusting them to judge your literary efforts, the least you can do is address them by name.
Check the Masthead or the About section on your target literary journal’s website for a list of editors. If you’re submitting poetry, just include the poetry editor (or editors) and the poetry readers (if they are listed). I like to end with “and the North Dakota Quarterly Team” following the list of genre-specific editor and reader names. You never know who might be paging through the slush pile!
Including editor/reader names in your cover letter isn’t going to convert a clear rejection into an acceptance, but it definitely can’t hurt your chances of getting a Yes.
Best of luck to you. Happy writing, happy publishing!