dirty bombs are totally ineffectual at anything beyond freaking people out per multiple studies. [1] the US wouldnt invade canada because canada is already essentially a client state that rarely doesn't bow to the US, and there is practically no added value in invading compared to the current arrangement. 90% of canada lives within 50 miles of the US border for a reason, and it aint just the weather. whoever told you this has no idea what they're talking about.

[1] https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/f...