Despite some cooperative ventures such as their pooled passenger service between Portland and Seattle and the Camas Prairie operation in eastern Washington, Union Pacific and the Hill roads Northern Pacific and Great Northern had been at odds for many years. I understand that one of the things which peeved the Hill roads was the fact that for several years, up until the postwar introduction of the streamlined Empire Builder, the quickest route from Chicago to Seattle by rail was to take Union Pacific's City of Portland  to its namesake terminal and then connect to service up the coast to Seattle. 

The Hill roads had managed to tick off Canadian Pacific as well. CPR was not pleased that Great Northern, with its direct connection to Vancouver from its main line at Everett, drew what it regarded as an unfairly large share of manufacturing and agricultural traffic from the American heartland to western Canada. Adding insult to injury, it was often faster for residents of eastern Canada to reach Vancouver by taking Great Northern's Empire Builder via Chicago than by taking CPR's more direct but also more difficult line through the Canadian Rockies.

So, at least in the 1957 Summer Tours season, the "Route of the Domeliners and Streamliners" and the "World's Greatest Travel System" found common cause. The "PNW" Pacific Northwest tourists would take Union Pacific trains and buses as far as Bremerton, Washington. After a Washington State Ferry ride to and overnight in Seattle, the group would be handed over to the Canadian Pacific system. They would board a Canadian Pacific steamship to Victoria, the capital of British Columbia, for an overnight stay at Canadian Pacific's Empress Hotel. The next day, they would depart on another Canadian Pacific steamer to Vancouver to board this train as far as Field, B.C.

There the tour group would board buses for a drive to and through Yoho and Banff National Parks. The exact itinerary varied for each specific tour group, but each would spend three nights in the Canadian Rockies at either Chateau Lake Louise, Banff Springs Hotel, and/or Emerald Lake Chalet. At four o'clock on day 12 of the tour the group would reboard the Mountaineer at Banff on their way back to the United States, connecting at Minneapolis with the Milwaukee Road's Morning Hiawatha for Chicago and home.

While the Mountaineer was a summer-season-only train, this route was not bereft of passenger service during the balance of the year. During the off-season a section of the CPR's Dominion split from that train at Moose Jaw and, under the name of the Soo Dominion, carried passengers along this route to and from the Twin Cities.