The list:
1. Winnipeg
2. Calgary
3. Detroit
4. Regina
5. Edmonton
I must technically correct myself, Manitoba is the top overall, not specifically Winnipeg. I know of several smaller towns with 7-11s, though the numbers have dwindled recently. Brandon has a couple, Portage has two, Selkirk 1, Dauphin 1 and possibly 1 up in Thompson, but mostly in Winnipeg.