Canada hasn't exactly dealt with this perfectly, that is true.
But the US has done one of the poorest jobs in handling this. If they're to send troops to stop people from crossing over, whether his motive is to "stop Canadians from crossing over to the States" or not, doesn't mean a thing to me. The States is rapidly becoming one of the highest infected countries, so keep them away, even in the guise of them trying to keep us away.
However, it wouldn't surprise me if his real motive (whether they say it or not) is to keep Americans in, not keep Canadians out. With his plan to remove social distancing and have people return to work to help the economy, I'm betting he wants to keep Americans in to prevent them from escaping to Canada. That's my opinion.