Given the importance to both the United States and Canada of the major railways linking coasts, it is hard overstate the importance of the completion of the Canadian Pacific Raiway (CPR). Built between 1881 and 1885, the CPR linked Canada's vast expansive provinces in a way that helped to unify the country, which was -- and to an extent remains -- deeply divided between Canadians of British and French heritage. (It should be noted that the railway actually falls short of reaching the Atlantic Coast, ending as does in Montreal) To suggest, however, that the CPR's completion ranks in importance with the formal establishment of the Confederation in 1871 is a little bit of an exaggeration.
The formal establishment of the Confederation was an essential part of Great Britain's long-term strategy for securing its hold on a major part of North America, and for unifying the French- and English-speaking provinces. Concerns regarding U.S. expansionism were high in Britain and in its remaining North American colony, and fears of U.S. support for French separatism helped drive the political efforts at establishing a quasi-independent Canada. From an administrative perspective, uniting the region under a single federation was needed to help hold the country together, as the distances involved were obviously great.
The construction of the CPR was a very important element in executing the mission of unifying Canada and securing its territorial sovereignty against the fear of U.S. encroachment. Its completion enabled British settlers and government officials to more rapidly and efficiently transit the country's expanse, while facilitating far greater levels of commerce among the disparate provinces. Its completion cannot be considered more important than the establishment of the Confederation; it should, rather, be considered a logical and necessary extension of the movement towards federation.