Fun stuff this morning on my return flight to Toronto. We were on the runway in Montreal (YUL) and then started our take off roll. Then all of a sudden as we were roaring down the runway, they reversed thrust and stopped the plane quickly. We were all a bit stunned by what had taken place. We exited the runway and they came on over the public announcement system and said that runway safety could not be guaranteed and that was why we stopped. So, for the shortest while we were on the taxiway and then I looked out the window to see an Air Creebec Dash 8 taxiing up the runway we were just roaring down. So, now I know what was meant. Everyone assumed that there was something wrong with the plane. Anyhow, good times for all. That was a first for me and I fly once to twice monthly.