If using canned chicken, drain excess liquid. In a big bowl, combine chicken, grapes, celery, onion, and almonds then mix thoroughly. In a separate bowl, combine mayo, sour cream or Greek yogurt. Dijon mustard, lemon juice, garlic powder, salt/pepper and mix together. Pour dressing over chicken mixture and make sure everything is mixed together. Can be enjoyed right away or in an airtight container in the fridge for 3 days.