Marinating Chicken before stewing it. Will there be a significant difference in the flavour?
Marinating meat is typically for fast-cooking methods like grilling.  

Typically when stewing, the chicken will stew for more than an hour, so any flavour from the marinade will be MOSTLY lost.  If you use a very strong marinade, like balsamic vinegar, you might retain a small bit of flavour in the chicken.  But keep in mind, the flavour will undoubtedly seep into the rest of the stew.

Overall there is usually not much point in marinating stewing meat, simply because you can impart all the flavour you want in the surrounding sauce, and tenderizing is done by the long cooking process.