why not just get a last minute all inclusive to cuba/dominican/mexico? It will probably be the most convenient and probably cheaper.
it will be fairly hard to find any hotels available on the east coast on such short notice.....decent motels/hotels I mean (not the stuff that gets 1-2 stars on trip advisor because of rats, cockroaches etc); and also they are really expensive! I just came back from Maine (Old Orchard Beach) which is 6h away and it's pretty nice but we were lucky to get a room that someone else cancelled....otherwise everything half decent was booked, even at 150-250$/night!!!!
In Atlantic city it might be easier to find something given there are many large hotels.....then again, Atlantic city has some really bad and shady areas that are right outside nice Casino-hotels so you'll have to see....personally I wasn't a big fan but if you stay in the touristy areas you should be ok.
And making it to Virginia beach in 10h is....let's say you'd have to drive REALLY fast
. Myrtle beach is 1800km away so it's more like 18 hours.
Other spots would be Wildwood and Seaside Heights (where they film Jersey Shore....maybe you'll be lucky and meet Snooky
), Rehoboth Beach in Delaware is not bad either.
In Canada you could go to Wasaga beach in Ontario or Parlee beach in NB.
For road trips there's tons of choices:
A nice USA 8night one would be
MTL-Washington DC (2nights)-Myrtle Beach(3 nights)-Tail of the Dragon(Knoxville area)2 nights-Harrisburg(1night)-Mtl