Need a better sense of what you're looking for... cost is the primary, or nice atmosphere, or location within Alexandria such as water....?
Royal Restaurant is good, low-end brunch. By the water you might look to Indigo Landing (used to be Potowmack Landing) though much nicer when it's warm and you can sit outside by the water. Stella's is an iDine...
If you want a nice lunch in Alexandira (closed Sunday), Bistrot Lafayette on King St offers a $16 3-course menu of classic french bistro food.