Ms. Sheppard might be able to correct me. While the standards might be worded slightly differently in terms of charges, I think they amount to more or less the same thing: the reasonable prospect of conviction and that it be in the public interest to proceed.
I think it's going to depend on local knowledge and practice. You have some crown counsels who are becoming specialized human trafficking prosecutors and, with that, you have their experience and familiarity with the provisions. Others may approve or go forward with charges they are more comfortable with, such as a prostitution-related charge, for example.