We love and sail the Chesapeake Bay year round, but you do not want to plan a cruise down here in July or August....it is just too hot and often no wind. Believe me, the Bay has fantastic cruising, many harbors, etc, but the prime sailing season down here is spring and fall. I would highly recommend Maine. It's probably one of the best cruising grounds in the world. The negative with Maine is the potential for fog...especially in late July/August. Cape Cod and the islands are also great, but very busy in summer after July 4th. You could probably get a great deal in the British Virgin Islands since it's off-season. The weather and winds would be good and the cruising is outstanding. As a final alternative (that I'm familiar with), you could cruise from Boston, MA to Portland, Maine...many great cruising stops in between without risking the fog of Maine (further down east) and avoid the crowds of Cape Cod. Great stops along the way from/to Boston would be Scituate, Marblehead, Salem, Rockport, Portsmouth NH, and Portland among many others.
Anyway, just a few ideas. If you advanced you vacation time to May-June or Sept-October, then the Chesapeake Bay would be fantastic and you could attend the Annapolis Boat Show in early October at the same time (Columbus Day weekend), definitely not in the summer IMHO.