How does a speeding ticket in Canada affect me as a U.S. citizen and driver?

I wouldn't ignore it, but there may be no reciprocity with your state. As an example, I am a MO driver and have a bit of a lead foot. I got a ticket in Ontario, but found out that there is no reciprocity with my state (though there is with NY, MI and a few others, allegedly.) Thus, I didn't worry about points and simply paid the vig, and boy was it a vig - $270 just to pay the speeding ticket for less than 120KPH in a 100 zone. I would never recommend simply paying the fine in Missouri, because the points will kill you with insurance increases, possible suspensions, etc. Save the points for jurisdictions, such as much of Illinois, where you can't simply bribe the court for no-points recommendations. (Oops, did I say bribe? I of course meant a legal recommendation to a non-moving violation of illegal parking even though you are speeding not parking...) Etc.

I am quite sure that it will cause you problems if you are planning on going back to Canada anytime soon. It is my understanding that Missouri does not put points on your license for tickets of this nature. Canada is not going to come after you either. Not for a speeding ticket.

My guess is that Canada would issue a warrant and if you ever tried to enter the country again you would be arrested. I wouldn't be surprised if it gets you on a no-fly list as well. Canada is VERY serious about criminal issues.