On my recent (August 2013) trip to Montreal, my girlfriend and I snagged a bunch of products you can't get in the U.S. (or that I'd never seen, at least).
The Reeses Oh Henry was really good, as was the crunchy Reeses. I'd read about the Coffee Crisp and the Smarties (which, in Canada, are similar to M&Ms), but they're too milk chocolatey for me. In the U.S. there's a dark chocolate Kit Kat, but it's got to be like 51% or something significantly less than the 70% they're giving the Canadiens. That being said, I have to admit I actually like the American version better.
The really good stuff was Lays funky new flavors. They did a contest just like this in America, where Cheesey Garlic Bread (stupidly) won over Chicken & Waffles (yes!) and Sriracha. But in Canada the contest still rages between Creamy Garlic Caesar (which doesn't taste different enough from Sour Cream and Onion to matter), Maple Moose (which is a mesquite maple flavor that's even better than Chicken & Waffles was and is just amazing. It tastes like maple pancakes that you cooked while camping), and Grilled Cheese and Ketchup (which was also so good! I don't even like ketchup! The best thing about them was that I mixed them together with a bag of dill pickle flavored chips from America, and they tasted like a McDonalds happy meal cheeseburger.) It's hard to choose between Maple Moose and Grilled Cheese & Ketchup, but while you don't have to, go to Canada and pick up a few bags each! Fortunately, Fries and Gravy is a regular flavor (it's a poutine thing, I assume), and it's awesome. We also tried the Bacon Hickory Potato Stick Juliennes, and they're pretty good. They kind of taste like a can of bacon baked beans.