Citizenship is not a requirement for certification. Completion of education, training, and successful examination are the determining factors in gaining certification. You are not eligible to sit for the Certification exam to become a Certified Anesthesiologist Assistant (CAA) without matriculation and satisfactory progress toward graduation in an accredited anesthesiologist assistant program.
Regardless of your prior training or experience in another country, all candidates—both non-US citizens and US citizens—must meet this requirement. The NCCAA maintains this standard to ensure all candidates have received education and training that meets the specific criteria established by CAAHEP for anesthesia education programs in the United States.
See Eligibility.