As the authors make clear, this 1950s HMSO publication data is derived from a very mixed bag of sources. The earliest years are based on returns to local customs officers designed to ensure that departing ships had adequate provisions to see them through the voyage. Persons travelling on business or for pleasure, as well as immigrants, were likely counted. That's why the term outward movement rather then immigration is used.
Having no Irish roots I had overlooked that the Irish were the major component in the early years, about until Canadian Confederation in 1867. According to the LAC online exhibit The Shamrock and the Maple Leaf "Approximately one million Irish landed in Canada in the century before the First World War." As expected there's a huge increase at the time of the Irish Potato Famine, with the English and Scots increase likely being Irish coming through their ports. The Irish immigration to the US at the time was much larger. An earlier increase, in the 1830s, is likely associated with the immigration stimulated by the Poor Law amendments in 1834.
After Confederation the English are the major component, including in the large pre-WW1 spike, which will be the topic of my OGS presentation. The drop during WW1, and following restrictive immigration policies to protect jobs during the depression of the 1930s, is clear.
The reference is: External migration; a study of the available statistics, 1815-1950 / by N.H. Carrier and J.R. Jeffery -- London : H.M. Stationery Office, 1953. -- 163 p. ill. -- AMICUS No. 12298747.