To come to Canada from the United States, you have to fit into a narrow exception from the Safe Third Country Agreement. That includes things like having family members in Canada. It's perfectly reasonable for someone who is a refugee, who happens to find a way to the United States, to want to come to Canada to make a claim here instead of in the United States. So there's no real rational reason that person shouldn't be able to get access to an appeal.
I think it's particularly important—