Literary Managers and Dramaturgs of the Americas (LMDA) is an association for Dramaturgs.
LMDA has published a set of Employment Guidelines for dramaturgs, and a series of Sample Contracts for some of the many ways that dramaturgs are hired. The Guidelines have info in rates that LMDA has found via surveys, but the organization is not a union and doesn't publish suggested minimums because the range of contracts are so varied. Dramaturgs are not part of the CTA/ITA.
LMDA is an organization that services dramaturgs across the Americans but it also has a separate Canadian chapter that represents Canadian dramaturgs.