What sort of things do you enjoy doing/seeing?
Bruges and Amsterdam are both lovely cities. Amsterdam has a very compact, pedestrian/cyclist friendly centre and there are some lovely myuseums and art galleries (I particulalrly loved the 'Kattenkabinet' which is what happens when you have a very rich, cat;loving art-collector...)
You can get to either Brussells or Amsterdam fairly easily by train from Paris - it's about 3.5 hours to Amsterdam, 2.5hours from Paris to Bruges. Paris-Brussels is only about 1.5 hours so you could even do a day-trip if you wanted, and have a longer stay in Amsterdam separately.
Italy would take a lot longer - I think 7-8 hours by train, although of course there will be (fairly) cheap flights, too. Persioanlly, unless you are thinking of going for 3-4 days I think I'd focus on amsterdam/Bruges/Brussels rather than Italy, as you'll have more time for doigthing rather than spenind hours and hours on trains or in airports.
Enjoy your trip!