Final answer:
British Columbia joined the Dominion of Canada in 1871, allowing the country to extend from the Atlantic to the Pacific Ocean.
Step-by-step explanation:
The province that joined the Dominion of Canada in 1871, allowing Canada to reach the Pacific Ocean, was British Columbia. This was a significant event in Canada's history as it marked the country's expansion from coast to coast. The agreement for British Columbia to join the Confederation was contingent upon the construction of a railroad, namely the Canadian Pacific Railroad, which would connect eastern and western Canada.
The stipulation was that the railroad should be built within ten years, which was indeed accomplished, with its completion in 1885. This railroad played a critical role in the development and settlement of the prairie provinces and the industrialization of Canada.
The province that joined the Dominion of Canada in 1871, allowing Canada to reach the Pacific Ocean, was British Columbia. British Columbia agreed to join the Dominion of Canada if a transcontinental railroad connecting eastern and western Canada was built within ten years. The Canadian Pacific Railroad, completed in 1885, played a vital role in connecting the country and aiding in its industrialization.