I have received the following explanation after calling the TurboTax help line. I hope this clears thing up for all who had a similar question to me.
T2125B = business income
T2125P = professional income
T2125C = commission income
T2042 = farming income
T2121 = fishing income
The numbers 1-4 in each category correspond to the numbered business or professional activity you have listed. So if you are self-employed and only have one business, choose T2125B #1. If you have multiple, T2125B #1 for income related to Business 1 and T2125B #2 for income related to Business 2 and so on.
