I have heard that it is impolite and improper to apply to a masters/PhD program and ask more than one professor at that university to be your supervisor. In other words, when you apply to a single program, you should have determine who you want your supervisor to be and apply upon the prospect that if that professor doesn't want you/need you, you will need to apply again at a later date with a different supervisor.
What about applying to different institutions at the same time however?
Would it be harmful in any way to apply to programs in different universities, either on the same country or internationally?