I don't know how the EUrosocialist countries (including Canada) are going to keep polygamy out. I'm not so sure we can keep it out for good in the US. Utah is kind of a special case, because their state constitution explicitly forbids it, and their state laws forbid not only multiple marriage but even multiple cohabitation. However, AZ has a lot of polygamists, supposedly, because AZ law is more lenient.
Sooner or later the Utah/AZ polygamists are going to hook up with the Muslims & file the mother of all lawsuits, and then voila.