The difference between the two can be seen below (the post it is from is an experiment comparing corn meal and flour used in anadema bread):
The corn flour is the white, finer ingredient on the right. The first obvious difference is that the texture will differ between the two. The second is that it would have different uses. Both would be effective at displacing gluten-containing flours (as in, neither would be helpful in gluten formation).
In terms of substitution, however, corn meal is likelier substituted by something like semolina flour and corn flour is likelier better substituted by quinoa or garbanzo bean flour.
