Unless you are leaving in the dark, I don't see this as an overnight trip, unless you are under a lot of time pressure. I agree with capecodda: you can make it in one shot, but its about 55 miles to the Mass Bay end of the canal, which would make for a very long day. Scituate is a great stop and is "easy in, easy out", compared to P-town, but it's not that far from Salem. You might consider Plymouth for an overnight, taking a mooring inside the harbor or anchoring further out.
The current at the canal turns fair (to the west) around 1:30-2:00 PM on July 20-21, so you might plan your arrival at the Sandwich end of the canal NLT 3:30 PM. My guess is that you'd have to leave Salem before 5:30 AM and maintain 5kts to have a chance of arriving at that time. You would still have another 2 hours before you'd be at anchor in Onset. It's doable, but it would be a slog.
You want to time your passage through the canal for a fair tide, but avoid the maximum currrent. I've been through a half dozen times or so and one time caught it at max. current (7 kts current, SOG = 11.5 kts!) as I passed by the west end. The eddies made the trip more interesting, but it's a good thing the RR lift bridge didn't come down in front of me!
Agree with Onset as a good stop. You can anchor or pick up a mooring at IPYC or Onset Marine. If you keep going into Buzzards Bay on a fair current, you may be opposing the typical SW breeze and could find it a little rough along the Hog Island channel.