My reading of this is that the Army is there to assist your Border Service in "welcoming" the "refugees"...not to prevent them from entering Canadian soil.If I'm correct on that it would be in keeping with Trudeau's "open arms" policy.
If you turn them around at the border, they end up back in the US.
I think if they succeed in setting foot on Canadian soil at a place other than an official crossing your people couldn't return them to the US without breaking a treaty.And of course if the situation was reversed the same treaty would prevent us from returning a person to Canada.
As I posted a day or two ago there's a town in Vermont called Derby Line which is on the border with Quebec.I've visited the town several times on my way to Montreal.There's at least one spot in the town (The Haskell Library...google it for interesting info) where one can easily cross from US soil to Canadian soil.In fact I once had a short chat there with an RCMP officer who was about 20 feet inside Canada at the time...with me about 1 foot inside US territory.That was a first for me..an international conversation with the use of wires.
And that's where the treaty and,it would seem,Trudeau's open arms policy comes into play.
But fear not...winter should thin out the herd heading north.
Let's hope.