Shimano indexed road and mountain front derailleurs use a different cable pull ratio, and that's gonna be a problem for you: MTB derailleurs don't exist with proper cage radius for a 52-tooth chainring. Road derailleurs do, but they won't have the correct cable pull to index with your MTB shifters.

In addition, while there are top pull road derailleurs for cyclocross bikes, I'm not aware of any that have a shaped cage for a triple. (If the derailleur has a big enough swing and a long enough cage, you may be able to make a double front derailleur work.)