WASHINGTON -- Wisconsin Gov. Scott Walker (R), a staunch advocate of beefing up security on the southern border, said Sunday he is open to building a wall on the U.S. border with Canada as well. The Republican presidential candidate said the idea of building a northern wall was brought up to him during a recent town hall in New Hampshire. "That is a legitimate issue for us to look at," Walker said Sunday on NBC's "Meet the Press." Republicans typically take a tough approach on securing the southern border, but few have said a wall should also be built along the U.S.-Canada border.