>>I would imagine, the safest communication would be to transmit from Canada or elsewhere with amateur receivers in the USA. Smuggle messages to the transmitter and everyone listening could hear if it wasn’t being jammed.<<
You mean from Canada from Ham radio?
I’m really close to Windsor.
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.