I can't seem to find anything about klan numbers in Canada. Despite the lack of lynchings, etc., I think the 250K is reasonable.

They claimed 70,000 members in Sask alone
http://www.usask.ca/education/ideas/tplan/sslp/kkk.htm
Emmons and Scott spent most of early 1927 crisis-crossing Saskatchewan spouting Klan propaganda, burning crosses, selling memberships in the Klan at $13 a head, and establishing local Klans in several centres. Emmons and Scott made one final sweep through Saskatchewan and then disappeared from the province taking with them the Klan funds.

With the scandal caused by the sudden disappearance of Emmons and Scott, the Klan in Saskatchewan should have lost its popularity. However, it floundered but survived under Dr. John H. Hawkins a Klan organizer from Virginia, and J.J. Maloney, a one-time Jesuit seminarian from Hamilton, who believed he had a mission to "denounce the errors of Romanism".

Throughout 1928 Klan lecturers travelled around Saskatchewan and it is during this period that the Klan reached its moment of greatest prominence. Klan organizers claimed a membership of more than seventy thousand by the end of the year! While it is likely that this figure is greatly exaggerated, the Klan did raise fifty thousand dollars from membership fees and other donations in the province.

They blend in. We had one klan member on our street. He was a busy-body whom all the kids despised. We also had one black family -- the first to get cable TV, and very popular with the kids because their kids could invite you over for that incredible treat: American Saturday morning cartoons. Recently, a clan-sympathizer ran for mayor, and hardly anyone seemed to notice (I suspect because she had no chance and the media didn't want to give her ANY publicity to her views).

As for Indian Residential Schools, 1950s was too limited. There are pleny of hits on the web. Here's one quote: "The Anglican Church administered 26 such schools between 1820 and 1969" Stats Can says there are about 12,300 claimants with an average age of 57.

More recent: (http://www.canadiancontent.ca/articles/031401reddog.html)
By the spring of 1979, the Klan opened a public office in the Riverdale neighbourhood of Toronto. Although McQuirter declared the Klan to have over 2,000 members across Canada, police sources reported that membership was only about 70 and that newsletter subscribers peaked at approximately 200.

I hope things haven't become too much worse.