Have you considered the singlescruise.com Canada cruise from NY? That's on the Triumph from 7/2 - 7/7. It's a little shorter than the Halloween cruise, but sounds nice. I'm booked on that one with a friend. I live in FL, but am originally from NY and have relatives who I can stay with up there. We're going to spend a few days in NY after the cruise to enjoy a little of the city, etc. too.
By the way, my friend and I are both single women, late 30's. This will be my 10th cruise, 5th on Carnival. I went solo on a cruise in Hawaii with another singles group this past December and had a blast.
You might find the weather quite hot for the July cruise to the Bahamas. The Halloween cruise is at the very end of hurricane season. I've cruised to those ports around that time and the weather was fine. However, you do run the risk of storms at that time of year - ship may be re-routed or worse. If you do select the Halloween sailing, be sure to purchase the travel insurance, just to CYA.