Well, yes, it would be nice if these trip planners did account for the closed border, but I'm willing to give them a bit of slack considering the COVID-19 restrictions are somewhat unique. I suppose it would be reasonable to expect a setting to disallow border crossings like it can to avoid toll roads and ferries, but again, this would be a fairly unique situation. Depending on where in CT and MI you are starting from/going to, under normal circumstances you would absolutely want to navigate through Canada to save hours worth of time.
You can always set "avoid" Superchargers in ABRP, and while I suspect this would work, it's not the easiest solution as you would have to set this for many Superchargers until you got a Canada free route. The solution to simply add a waypoint in Toledo, OH seems simplest and very straightforward. I wonder why you think that is difficult.
If this were me (and to get to your final question about whether the in-car nav would allow you to avoid Canada), this would be my workflow:
I am a big ABRP fan, so that is my preferred/primary routeplanner. The car's built in route planner is quite good as well, but I actually trust ABRP's more as it gives more relevant information, actually seems more accurate, and allows me to easily select alternative charging stops. So I always start with an ABRP plan and run it on the car's browser. Once I see the next charging stop, I will "share" it with my car (or just manually navigate to that Supercharger using voice commands) so that the car's navigation also displays the route and will pre-condition the battery as necessary. So normally the car doesn't have any idea what my final destination is (when I'm one or two Supercharger stops from home or final destination I may eventually put that into the car).
In your case, even if you wanted to use the car's nav system, and you knew you would be going through Toledo, you could just ask the car to navigate to Toledo until you got to a certain point (Wilkes-Barre, PA maybe?) where it would certainly not route you through Canada, and then use your actual final destination.