A few issues come about from this.
1) Canada's Tax Law's do not make non residents pay tax (down here every American needs to pay tax to the USA, regardless of residency. The only exception is when there are tax treaties, and you are getting taxed elsewhere (like Americans living in Canada, not that I understand why they would...)
2) Canada's Dual Citizenship issues, which have been hashed out here many times before.
3) The costs of Repatriation to Canada - especially when this has been done previously.
4) The belief that Dual Citizens can then import their families who aren't Canadian Citizens
Probably none of those issues by itself would be a significant problem - but when combined they make a rather significant issue for Canada.