Forgot a couple of things.
1 I have done part of the Trent-Severn in a powerboat only, but have talked to people who have done it in a sailboat. It is nominally good to 5' and they both had that draft but hit things in the channel several times, including things more solid than mud. I would likely not choose that route with most cruising sailboats unless draft was closer to 4'
2. The route you pick should be related to where you want to go once you reach the ocean. If you want to get to eastern Caribbean (BVIs down to Grenada), you are either doing the ICW all the way south and then the Thorny Path or you are going offshore from the Chesapeake or somewhere else. If the latter, the Mississippi route makes no sense. If you were going to the western Caribbean, the Mississippi route makes a lot more sense.
Heading back to Lake Ontario for this summer. Now in Bermuda and heading to Long Island Sound in the first week in May. Then on to the Hudson and the Erie Canal.