What is my liability if someone else in my group tries to smuggle contraband through customs?

Im organizing a trip across the border to canada with a fairly large group of friends, some of which i know well, some not so well, now knowing that a few of them are big weed smokers, im going to do my best to make sure no one brings anything across that can have problems, with the nature of our trip being one that will certainly have us pulled over at customs, i need to know, how much trouble can i get into, if someone is found to have anything illegal on them, when i do my best to prevent that from happeneing?