Possible Clues:

• Thunder Bay’s prov
• Province abbr. within "Toronto"
• It's on the St. Lawrence: Abbr
• London's locale: Abbr
• It shares a 1,650+ mile border with the U.S.: Abbr
• Third largest Prov
• What's about 150 mi. north of Duluth
• Mich. neighbour
• Province by N.Y
• Prov. west of Niagara Falls