One of Canada's most famous treats is coming to the U.S. for a day — even if many Americans have never heard of it. Tim Hortons will celebrate Canada’s 150th birthday on Saturday by offering a poutine doughnut at five of its restaurants. A poutine doughnut is one the chain's Honey Dip Donuts topped with potato wedges, gravy and cheese curds. (Poutine is usually made minus the donut.)