Rule #1 of SDN, if a pre-med answers your question ignore the answer. Several pre-meds gave their 2 cents, and while their intentions were good, this is how false information gets spread around SDN and thus the internet.
I will say first off that I know little about OB/GYN. I have zero intention of doing anything OB/GYN after my core rotation. However, I can speak about IM and Gen surg (to some degree).
It really comes down to ACGME Vs AOA (or soon to be "ACGME"). Lets start off with the AOA sites (same sites that will get ACGME status within a few years). For IM, Cards is doable if you were to do a IM residency at program with fellowships. A lot of it can be word of mouth and how well you get along with people. Gen Surg AOA is also quite attainable if your COMLEX is decent (you said average student and nothing about board scores).
ACGME: Gen surg impossible. Don't waste your money on apps. IM is much more attainable, but as an average DO student expect low-tier IM residency spots. Maybe "mid" tier. (mind you this whole tier thing is relative to you speak to, so i wont even bother listing examples of each tier). However, in order to get cards afterwards you need to be in a decent university program with fellowships. You could also be in a community IM program that has a high fellowship match rate. (there is one in Portland for example).
Hope that helps, good luck!