It depends on you're interests, you will have to do heaps of calculus, analysis, etc if you decide to do a maths degree (and will only get to do a few courses related directly to game theory), and if you decide to do straight economics, there will probably be only one or two upper subjects titled 'game theory' (allthough parts of game theory is usually covered in a section of each of the microeconomic theory subjects).
But ether way you wont get to do pure, and proper, game theory until the later stages of ugrad, and you will need a good understanding of mathimatics if you take grad level game theory courses.
But It seems rather odd that you already know you want to do 'game theory'...and it's not an industry you 'work in', rather an area of research.
Anyway you might want to look into the ANU science degree which offers a major in mathimatical economics, or UNSW economincs/mathimatics, or Melb Uni BCom (major in economics) with breadth in mathimatics