Three places come to mind
Zebra in Southpark
131 Main in Dilworth
Pewter Rose in Southend
Zebra is most fine dining option and they have a very nice breakfast/brunch menu. They are chef owned and with a group of 40-45 people I suspect you will find most owners very eager to please. What time shall I be there and is the happy couple registered?
What price point? I think you're wise to shoot for mid-day when most restos typically have a lull in business.
Trio is very accomodating for larger parties and reasonably priced. They will print up menus for you limiting options, if you so desire. They could do the main dining area or that semi-private one downstairs. Lots of food options too; salads, sandwiches, brick oven pizzas, soups and entrees. www.trio-charlotte.com.
A higher end option would be Ratcliffe on the Green, as waitress mentioned. I'm also a huge fan of Lulu's but I know they no longer do lunch during the week but not sure about the weekend.
here is a thread from a similar question not too long ago
If your guest are out of towners, maybe uptown would be best, if money is no object, Radcliffe on the Green, LuLu's on Central, Savannah Red in the Marriott is super nice and you would rule the whole space, but it is dark in there. Maybe something that opens into a patio would be really nice, depending on the month.
Some restaurants on East Blvd. A Saturday mid day, most restaurants would love the business, so I don't think you will have any trouble booking it. Casual theme, could be Cantina 1411 on East, margaritas and bloody marys sounds fun. There is also South Charlotte to consider, Nobles or Roosters.