How to make reservation on IC train for Milan to Stresa if I arrive on same day?
 

I'll be flying into Milan, and taking the InterCity train to Stresa.

Also read that reservation on IC train not required, but recommended. But if I'm arriving in Milan from London at noon, and take the train from Milan to Stesa right away, that doesn't give me time to make reservation inside Italy. I also don;t think you can make reservation over the web? so what are my options?

I assume you're landing at Linate Airport (NOT Malpensa) and taking the airport bus to Milano Centrale, whence you plan to board the Intercity to Stresa??????

When you arrive at Milano Centrale, get on the first available Intercity train to Stresa. If the train ORIGINATES in Milan (rather than in Venice, for example), you should have no problem finding a seat, even in second class. It's only a 50 minute ride. If you're concerned, buy a first class ticket. If you happen to board a French CIS train (Cisalpino) bound for Stresa, you will probably be required to pay extra for the mandatory seat reservation.

If you're landing instead at Malpensa Airport, be aware that there is direct BUS service to Stresa, on a reserved basis, which operates daily through October 5 or thereabouts. This is more convenient (and cheaper) than taking a taxi to Gallarate Station and thence a local or IC train to Stresa.

Be very careful to board an Intercity train that STOPS in Stresa! A few IC trains skip Stresa and stop only at Verbania, which is several kilometers further north. Ask the ticket agent whether the IC train you intend to take stops at Stresa.

GAC:

Thanks for the info. I'll be arriving at Linate, and there I'll take a bus/shuttle to Stazione Centrale.

Reservation on italian IC trains is not mandatory, so if you catch an IC at the latest moment and you have a valid ticket (that is ticket plus IC supplement) you will have no problems and you can sit wherever there are seats available (not reserved or taken).
I have taken lots of trains on the Milano Centrale- Stresa route and in the late afternoon, let's say around 5-6 pm these trains tend to be a LOT crowded because of the commuters that go back home from the offices in Milan. So that could be a problem if you have suitcases. So if the train originates in Milan and if you have time to arrive at the station quite ahead of the departure, I advise you to get on the train soon and take some seats that are not reserved.
I have also taken the Cisalpino train, but you need to pay a difference in price and get a seat (which is mandatory). Sometimes if you ask for a seat reservation at the latest moment at the ticket counter of the Centrale, the clerk will tell you that he is not going to reserve the seat because they have closed the reservations and that he will only issue you the difference in price between the IC and the CIS (Cisalpino). True ...BUT if the computer doesnt give him any seats to reserve because you are much too close to the departure of the CIS, he should also tell you to go and find the ticket man of the swiss railways ON the train as soon as you get on the train or you will get a fee. So when you get on the CIS you will need to find a the ticket man of the swiss railways and tell him all this and he will reserve a seat there (it costs a little more though). This is what happened to me twice.