Why Canada's pot legalization won't stop black-market sales

ake Rowinski, a 20-year-old University of Toronto student, buys marijuana every week from one of the many self-described “medical” dispensaries in downtown Toronto.

“Nobody really cares at this point,” Rowinski said outside the shop, near the city’s financial district.

As Canada’s Liberal government prepares to legalize recreational marijuana use this summer, the biggest remaining obstacle to regulated sales will be competition from a thriving black market, according to cannabis investors, researchers, policy analysts and government data.

Many buyers of illegal pot will have little incentive to switch to legal weed,...