Correct on all counts. I don't know how much control Quebec City has over international[1] tariffs, however.
So the shocking allegations boil down to
* US attempt to talk to Quebec City about tariffs, and
* a US think tank publishing something in February 2026 about how the US might benefit from the (meaningful, longstanding, legal) Quebecois pro-sovereignist sentiment.
Meanwhile, no shortage of announced Canadian intentions, in the first Trump administration and during the current trade war, to "target the red states" with tariffs to influence US politics, and no shortage of self-hating American Redditors cheering this on because Trump = bad, so anything that other countries do against the US = good.
[1] I have to specify this, because Canada does not have internal free trade! In some ways, trade with the US is freer than intra-Canada trade. Yet more proof of how as Paul Krugman wrote, Canada is closer to the US than to itself <https://krugman.blogs.nytimes.com/2010/01/13/eh/>.