rkjthguakj is pretty much correct, although I'd add that I don't think you'd have enough credits in your BSci alone to
technically do all the subjects in a BCom major - You generally have up to 6 breadth and this would require 2 level 2, 3 level 3 and 2 prerequisite level 1 subjects,
this pretty much explains what the major entails pretty well. But if you plan carefully (I.e. check out the
"what will I study" sample plan and try to find in everything you're interesting in keeping in mind prerequisites and semester availability from indidvidual handbook entries such as
this one), you can get pretty close and pick out which subjects best suit your purpose. But also keep in mind there'd be a certain number of level 1, 2 and 3 subjects you have to do for a
BSci in general.
As for a science minor, I don't believe science officially recognises minors (as far as I know only arts do this, but happy to be corrected if I've said anything incorrect). Similar to what rkjthguakj said above you can also probably technically do enough subjects for two majors with free science electives (would be easier if a major closely related to maths like mathematical physics or data science), but your transcript would only officially recognise the major you officially choose in your study plan.
That being said, this might also be difficult if you want to use all your breadths on economics. Another option could be to do a BSci in the other major you're interesting in and do a
concurrent maths diploma if you're super keen on exploring all these different areas and don't mind possibly having to extend your degree. Although apparently you can't do this with data science, but I think it'd work with a physics major
Best of luck, hopefully this wasn't information overload.