The (sadly anonymous) History of the Vote in Canada produced by Elections Canada in 1997, puts the period starting in 1920 in a chapter entitled "The Modern Franchise." With good reason.
The Elections Act of 1920 produced a largely independent-of-government elections organization headed by the new Chief Elections Officer. It also re-established a unified federal franchise, largely the same for all provinces, and confirmed women's right to vote throughout the country. First Nations people remained without the vote unless they gave up aboriginal status -- in effect, there was a certain recognition that First Nations had a nation-to-nation treaty relationship with Canada and were not precisely citizens as other Canadians. Various racial exclusions first established in provincial law were also reaffirmed: a BC provincial law disenfranchising Chinese and South Asian Canadians was carried over into the federal franchise for BC.
The 1921 election contested under the new electoral rules has 3.1 million voters, up from 1.8 in the hotly-contested 1917 election. It had the first national party leader who was not accountable to the parliamentary party caucus: William Lyon Mackenzie King, who had been chosen by a national convention of delegates after Wilfrid Laurier's death in 1919. (There would be no more Liberal conventions until King resigned from office in 1948, so as party leadership King was effectively accountable to no one -- certainly a hallmark of the modern era in Canadian politics.)
The 1921 election also produced the first third-party with nearly national reach and, not surprisingly, the first minority government. The Progressives, a farmer-labour-free trade-protest amalgam, ran a broad slate of candidates and elected 58. (First woman MP: Agnes McPhail of the Progs.) King's Liberal formed a minority government with 116 seats in a 235 seat House, and survived for four years.
1925's election confirmed -- nota bene, 2011 -- that the party with the largest bloc of seats has no automatic right to form a govenment The Conservatives, led by Arthur Meighen, who had succeeded Robert Borden, won the largest bloc, 116 seats in a 245 seat house. King, whose Liberals had 99 seats, concluded he could continue to govern, for he expected to support from the Progressives who had fallen to 20 seats. But in the House the Progressives soon decided to abandon the Liberals and put the Conservatives into office. The minority Meighen government succeeded the minority King government
Change of government without an election -- more news for 2011! 'Course the public didn't much approve, even then. When Meighen's fragile minority government fell in 1926, King largely campaigned against Governor General Byng, who had put Meighen into office by denying King a fresh election in 1925. Note to 2011: we still need a Governor General who is accepted as a legitimate actor in these situations where the head of state is required to determine the will of the House of Commons.
The Liberal Party in 1926 re-assembled the old Laurier coalition -- solid Quebec, farm support in western Canada, and enough of rural Ontario -- and put together a majority (by absorbing just enough Progressives to have a semi-coalition) that would endure until 1930. NB: Liberal majorities are always made on the left.
