How often does canada-us border close

How often does canada-us border close?
I have to catch a flight out of buffalo, but I am coming from canada to the buffalo airport. What are the chances that the border will close for some random reason? Does this happen often? thanks!
Other - Canada - 4 Answers
Random Answers, Critics, Comments, Opinions :
1 :
I grew up in Niagara Falls and in the 43 years I lived there I never saw it close. Its open 24/7.
2 :
As long as you plan on using one of the "Major" border crossings you'll have no problems at all. Some of the smaller less used crossings to have night time closures.
3 :
I don't know!
4 :
They closed the Peace and Rainbow Bridges for about three hours after the 911 attacks. That is the only time I can ever remember them closing.