Since you're taking an advanced science degree and planning to major in statistics or financial mathematics and statistics, you are expected to take advanced units (at least from second year on-wards). Most people in your degree planning to complete those majors would have scored high in 3U or did reasonable in 4U, and start taking advanced junior maths units. Even the mainstream units (MATH100X) are geared towards 3U students.
For your degree and proposed majors, you would need to at least complete the mainstream junior maths units with credit average (65+) in MATH1003 Integral Calculus and Modelling and MATH1005 Statistics, which would be sufficient for you to enrol into second year advanced statistics units. So you really should probably enrol into a 3U bridging course if you can.
But not doing a bridging course? That's doable if you apply enough effort. MATH1003 and MATH1005 aren't really that difficult if you aren't afraid of the mathematics. But a bridging course would be helpful. Alternatively or additionally, you can even prepare yourself by studying the following 3U topics on your own:
- Permutations and Combinations (highly relevant to MATH1005)
- 3U integration techniques (very relevant to MATH1003)
- Applications of Calculus (very relevant to MATH1003)
(Even though both MATH1003 and MATH1005 are both semester 2 units, now is an ideal time to start practicing some mathematics and building up some confidence in independent study. It's also worth noting that apart from permutations and combinations [and mathematical maturity], 4U students don't really have any advantages in MATH1005/1905 over 2U students.)
I don't know too much about Commerce, but majoring in finance and accounting seems to be quite a decent choice of majors; they both seem quite employable.
I would also recommend that if you're still interested in a statistics major but finding advanced units being too difficult or that mainstream units are enough for you, going from B. Science (Advanced) to just B. Science is a great option to still major in statistics without having to deal with the added difficulty and obligations of advanced units.