According to the official EC261 page:
If your flight is cancelled you have the right to choose between reimbursement, re-routing or return.
You are also entitled to assistance at the airport.
If you were informed of the cancellation less than 14 days prior to the scheduled departure date, you have a right to compensation.
So in your case you are not owed any compensation. You can ask for it (and if you are a frequent flyer with status or flying in a premium cabin you could possibly get a few miles/points), but there’s absolutely no obligation for the airline.
What often happens in such cases is that you receive an automated message informing you of the change of the flight directly affected, but it takes a bit longer for them to contact you about the rest of the trip (or in some cases nothing will happen until you contact them).
Your options are:
- to ask for a refund
- to have them change the other flight (or both flights) to have a better connection
- to keep the flights as they are and ask them to pay for the hotel and meals. Don’t go thinking you’ll be able to pick a nice hotel in central Paris and have them foot the bill though, they’ll send you to a hotel of their choice, most likely somewhere in CDG.
Flying MXP-CDG-BOS on a single ticket means you’re most likely flying Air France. This implies landing in 2F and departing from 2E (gates K, L or M). You’ll have to go through exit passport control, possibly security (though I’m not even sure). If your flight is on time, 1h55 is plenty of time for that. Even if your flight is up to one hour late it shouldn’t be an issue.
Beyond that it will become trickier, but as both flights are on the same ticket it is the airline’s responsibility you get to your destination timely, so:
- you would probably have staff waiting for you at the arrival gate to direct you to your departure gate, and possibly escort you through to make sure you don’t get lost or stuck somewhere
- they will probably hold the flight a bit if needed
If the incoming flight is very late and you can’t make the connection, they either have to reroute you (not sure there would be too many options) or arrange and pay for your hotel and meals. And since you would be delayed quite a bit, you would be due compensation in that case (unless extraordinary circumstances).