The New York Canal System (Erie Canal and others that connect to it) and Hudson River offer a great cruising experience. Head north from there and do the Trent-Severn Waterway, Georgian Bay... oh, goodness, you may need more than the whole summer. :wink:
The Hudson, NYC, and Erie Canal are easy cruising... interesting history in all the towns along the waterway. Easy access for staying on town/canal walls, supplies, restaurants, etc. It got warm when we were there in August, but not Florida hot/humid. Plenty of options for your shore bound friends in that area, and LOTS of day-tripping you can do with them.
North to the 1,000 Islands area between NY and Canada. Trent-Severn... cooler water, more open than the Erie Canal. Take that to the NW end and you are in Georgian Bay (30,000 Islands).
With that done, maybe it's time to sew up the rest of the Great Loop? SO MANY options.
As another option, pick any northern state, get some info from there, and hit every cruiseable lake.
You have a great boat - like a magic carpet to take you anywhere your imagination comes up with.
Best wishes,
Jim B.
And when you're ready to try the left coast (yes, I saw the part about not going west of the Rockies), Pat is right on about the San Juan Islands and all the other endless cruising in the Pacific Northwest.