You could smuggle messages across the border.....
.....a freedom loving Canadian Amateur Radio Operator could talk to another freedom loving Canadian Amateur Radio Operator so it isn't a "broadcast" (illegal in Amateur Radio, at least in the USA), and the information could be weaved into their discussion like a coded message.
But the Michigan border crossings would likely be shut down in such an "emergency". I was thinking about a country crossing west somewhere, where you could use an ATV or hike across in the wilderness into Saskatchewan for instance.
In some places “Downriver” (just south of Detroit), you can swim to Canada. A few hundred feet.
It’s where my DHs family used to row across to run rum down to Peoria.
If need be, you could send a radio controlled boat with a message to someone on the other side.