Re: Border wall
Let's assume this suggestion is halfway serious.
So we're building a border wall. A lot of this is in pretty rough territory that you first have to build access roads for to get the construction materials in. Secondly, imagine building a wall from Paris to Moscow.
The Canada/US border is not that long - it is four times longer. In fact because the border is not straight, and there's factors like Alaska to take into consideration, you are seriously looking at the equivalent of building a wall well over a third of the way around the earth.
By way of comparison, Hadrian's wall would get one sixth of the way across British Columbia, with all of Alberta, Saskatchewan, and Manitoba before we get to the Great Lakes ...
Much cheaper to just import refugees from the US as we are currently doing - at a cost of CAD 400 million per year. (Seriously)