NORTH TOPSAIL BEACH, N.C. — “APB... Amber Alert,” the tweet says, “where is Matt Canada?” Earlier this month, a friend sent Canada a screengrab of that message posted on the social media site, and on this rainy August day, it makes him chuckle. The tweet’s author is no one Canada knows. It belongs to that of a casual college football fan curious about the whereabouts of a college football coach who had ascended to the top of his profession and then, without a trace or goodbye, disappeared into the ether. The tweet wonders aloud what many of us have asked internally at some point this offseason: Where is Matt Canada?