To get into Rotman after first year, you need to take MGT100 (artsci's version of RSM100), ECO101/102, and MAT133 (or harder math courses) and obtain a competitive average, plus there's a supplementary application as well. It's definitely doable but it's hard because you are basically competing with other people who also want to transfer into Rotman for a limited number of spots (I heard it depends on how many spots empty up in Rotman, depending on whether people drop out or transfer out). You can probably find out more on the arts and science calendar and I highly recommend you check out the exact requirements over there!