Yeah you can only have a "specialization" in accounting if you are a business student, a minor is only for people who are in other programs.
Your major is Commerce and its up to you if you want to specialize in one of the business sub-sections.
As for the requirements I wouldn't worry about it too much. I got in with a 86% because they only count your top 8 uni level courses in highschool (this includes gr.12 uni level English and 2 Maths). TAKE ALL THE MATHS!! The one thing I regret is not taking calculus in highschool because they make you take an extra calc here at Mac if you don't have the gr.12 credit