Reports say that weed was found on one of Rihanna's tour buses when trying to cross the Canadian border. Apparently a total of 10 tour buses were stopped at Detroit's Ambassador Bridge when trying to exit Michigan into Canada. Cops said that they smelled marijuana on one of the buses and decided to do a bus-to-bus search, which resulted in a civil penalty charge for a passenger. Inspectors brought drug-sniffing dogs on the bus and one of them went straight towards a passenger and authorities found he was in possession of weed. They only found a  small amount of marijuana on the bus, and Rihanna was NOT on any of the buses. 

By the way, she'll be in town tomorrow night for her Diamonds World Tour! 

Source: TMZ