Hi Peter!
The Buffalo Stampede is indeed May 31 - June 1. I know there are several teams from Canada who compete. I may make that trip this year myself.
Others in the Uppper Midwest........New Holland, PA and Grand Rapids, MI are probably the only other close ones.
Check out the link from WyoJim..that will shed more light on the events.
I will also track down a link to the Canadian BBQ Association.