On what date did three British colonies unionized to form the federal dominion of Canada ?
What was to become the Colony of British Columbia was claimed as part of New Spain and Russian America , until 1793 and 1825 respectively , and was for a time shared with the United States as what was known to Americans as the Oregon Country , until in 1846 the border was extended west from the Rockies to the Pacific along the 49th Parallel .