If you have a strong interest in mathematics as a field and want to do commerce, do something like Financial Mathematics, Statistics or Applied Mathematics from a science degree (perhaps combined with Finance). Maths in a science degree really lets you explore the beauty of mathematics as opposed to an actuarial degree.
In the real world no one cares what degree you end up with, as long as you have the skills they are looking for. In investment banks for example, they look for people from a diversity of backgrounds including commerce, engineering, law, maths and physics (yes that's right, even people with a physics major are desired in banking!) simply because they tend to have the quantitative and analytical skills they are looking for.
I'm not sure about actuarial studies but most commerce faculties do NOT provide rigorous mathematical proofs to back up the models they use simply because it will freak the crap out of any non-maths people.
For example, in my Corporate Finance unit (from commerce) we basically got told, "CAPM looks like this etc etc" or "here's the formula for PV of an annuity" without even acknowledging that it came from a geometric series. In my opinion, it's pretty much "here's the formula, drill some numbers in it".
However in Financial Mathematics (from science) we actually derived the equations for CAPM from first principles to get the model using vectors, statistical and matrix theory which I found much more interesting and enhanced my understanding in terms of how to use it.