Major professional sports leagues in the United States and Canada
The Canadian Football League is the highest level of play in Canadian football. The league was organized in 1956 as a cooperative agreement between two regional leagues, the Big Four (which dated to 1907) and the WIFU (which was founded in 1936), and became independent from Football Canada in 1958. The league now consists of nine teams, all based in Canada. The Grey Cup is awarded annually to the champion every November and is the highest attended sporting event in the nation. The oldest extant teams, the Hamilton Tiger-Cats and the Toronto Argonauts, trace their origins to the late 1860s and early 1870s, which ranks them amongst the oldest professional sports teams of any kind still in existence on the continent. The CFL attempted an expansion into the United States in cities that had no NFL team between 1993 and 1995, though the expansion teams all either folded or relocated to Canadian cities.
Major professional sports leagues in the United States and Canada
The NHL has been the dominant professional sports league in Canada, and was first established in Canada in 1917. 
The NHL was initially based entirely in eastern Canada; by 1925, Hamilton and Quebec City no longer had NHL teams, while Ottawa would leave in 1934, by which point American teams were slowly being added. The first Canadian expansion team would come in 1970 with a team in Vancouver; the NHL later added teams in Edmonton, Winnipeg and Quebec City (through absorption of WHA franchises), Calgary (via relocation from Atlanta) and Ottawa (via expansion) to go with the still-extant Toronto and Montreal teams. The distinctive place hockey holds in Canadian culture allowed these franchises to compete with teams in larger cities for some time. However, the teams in Winnipeg and Quebec City were eventually moved to larger media markets in the U.S. The NHL returned to Winnipeg for the 2011–12 season, with the Atlanta Thrashers relocating to become the current version of the Winnipeg Jets. Excluding the CFL, the NHL is the only major league to have teams in Edmonton, Calgary, Winnipeg or Ottawa, all markets with fewer than 1.25 million, smaller than any U.S. NHL market except Buffalo. However, those Canadian cities benefit from the country's very high level of hockey fandom. A 2013 study by Nate Silver estimated that all of these markets had roughly the same numbers of avid hockey fans as U.S. markets with several times their total population.