Canadians Seek Ban on Americans' Drug Shopping By COLIN McCLELLAND     TORONTO (AP) -- Canadians must stop Americans from using Internet pharmacies to raid its medicine chest or face a drug shortage, a coalition of Canadian groups representing seniors, pharmacies and patients has warned.    The groups, claiming to represent 10 million Canadians, or about one-third the population, called on the Canadian government Monday to ban prescription drug exports...