The migrants have no option other than arrest. A longstanding legal pact between the US and Canada — called the Safe Third Country Agreement — means that migrants have to cross illegally if they’re coming from the US and want to request asylum. If they request it at an official Canadian port of entry, they’ll be turned away and told to make their claim in the US, where they arrived first.
https://www.businessinsider.com/asylum-seekers-fleeing-us-for-canada-champlain-ny-2019-1