It's a mostly open border and as has been proven in the past 2 years (people fleeing the US) it is easy to sneak across.
but here is an article:
Trump's Europe travel ban poses questions for Canada-U.S. border
James McCartenThe Canadian PressPublished Thursday, March 12, 2020 4:39AM EDT https://www.ctvnews.ca/health/corona...rder-1.4849675