After Ontario allowed convenience stores, grocery stores and 'big box' retailers to sell beer, wine, cider, coolers and pre-mixed drinks, 7-Eleven is pushing Saskatchewan to do the same. (The Canadian Press/Chris Young) Could Saskatchewan be the next province to OK the sale of alcohol in convenience stores? One major retailer wants the government to open up its policy on which businesses can get licensed to stock wine, beer and spirits.Lobbyist…