Canada and the Western US along the Eastern face of the Rockies are the prime spots on our continent to find fossils. That's not to say that there aren't any anywhere else; Kansas possesses a large assortment of marine fossils while New England is home to a few significant trackways and fossils have been found in New Jersey as well. The landscape of the ancient world is what causes things to be this way with the middle of the country being an inland sea for a good amount of time in that ancient world and the Rockies therefore being the western shoreline. When Barnum Brown, with this in mind, was searching for fossils in America and Canada, it was only natural that eventually he would work his way north to what is now Dinosaur Provincial Park in Alberta, Canada. Whether he gathered information from locals or from scouting crews.
Either way, in 1912 Brown, who would later travel to Greece and Africa as well and spy for the US at one point even, unearthed Corythosaurus. The specimens unearthed were so plentiful, so many ages and different specimens including one with fossilized skin were unearthed that at one point seven species of Corythosaur were thought to have existed, that some were even shipped to England to be place in the British Natural History Museum. In 1916 one shipment, 22 crates of fossils in the SS Mount Temple sent by Charles Sternberg, was captured and scuttled by a German merchant raider and still to this day lies on the bottom of the ocean. Coincidentally, the Mount Temple is already famously thought to have been the "mystery ship" which ignored the distress rockets of RMS Titanic on the night which it sank as the Temple was in the area and attempted to aid in the rescue.