Okay, I'll give this a reasonable guess. My theory, based on your hints, is that this bridge is at Hay River, which would make it significant in that it is the northernmost point in Canada and all of North America which is connected to the continental railway system.
Hay River is a town on the shores of Great Slave Lake, and is the terminus of the Mackenzie Northern Railway.
IF not this, then I am at a loss. I was thinking It may be the Deh Cho bridge near Fort Providence, But I believe that is a highway bridge only.
http://en.wikipedia.org/wiki/Hay_Riv...st_Territories :
Hay River is a community in the Northwest Territories, Canada, located on the south shore of Great Slave Lake, at the mouth of the Hay River.
Hay River is the northernmost point in Canada and all of North America which is connected to the continental railway system through the Mackenzie Northern Railway which interchanges with CN in Edmonton. The Alaska Railroad is located farther north but is orphaned from the network. It is in the South Slave Region.
Hay River has a population of 3,510, and the nearby Hay River Reserve another 269, according to the 2001 Census. It is referred to as the Hub of the North since the town is capable of sending goods by land, air and water.
Originally the end of the Mackenzie Highway, the relatively short Highway 2 links the town with this important northern highway. Airport and railway also serve the town, and it is the trans-shipment location for river barges downstream to the Mackenzie Delta.
The First permanent settlement in the area of Hay River was established in what is now the Katl'odeeche Reserve. This was sometime between 1892-93. This first settlement was established by Chief Chiatlo and a group of people by the building of log cabins and bringing dairy cows.
Hay River is also the home of NHL forward Geoff Sanderson.