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With a POD of 1900, have one or more religious groups get expelled from western Canada. This can be done via outright state-sponsored cleansing, ie. the military and/or Mounties show up and make everyone leave at gunpoint, or legally valid but still rather harsh immigration measures, eg. a group that had been issued entry visas suddenly has those visas revoked, with orders for all erstwhile visa holders to vamoose ASAP.

Push comes to shove, have a voluntary exodus, with the Canadian government arranging with some foreign government to host the sect, while offering attractive incentives for emigration.

Also, come up with some sort of background as to WHY exactly things reached a point where the Canadian government no longer wished to tolerate the group's presence.

Off the top of my head, candidates could include the Mormons of southern Alberta and BC(originally polygamists who had fled the US), the Hutterites of Alberta(who were subject to discriminatory land-purchase laws for decades) the Doukhobors of Saskatchewan and BC(I'm guessing the idea of kicking THEM out was at least entertained by several levels of government), and the Mennonites and other anabaptist groups.
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