Getting Bikes to Northern Italy?

The other option would be to leave your bikes behind, and hire them when you are there.  That will open up the travel options, and you may save enough to almost pay for the bike hire.  

Helicopter 

When I was a lad we used to cycle to Italy to have to have cycle holiday in Italy. People don't know they're born these days.

Lake as in Como or Garda?

Anyway, I take the train from London to Milan every year for the Italian GP, changing in Paris, which involves getting from Gare du Nord to Gare du Lyon. It's great, barely any slower than flying, much more comfortable, has no luggage limits and is often cheaper. Do it!

Cycle provision from Paris onwards is great, however the Eurostar leg of your journey is, predictably, a shitshow. You have to trust your bike to the care of EuroDespatch; they might have it in Paris when you arrive, or you might have to wait several hours. Iff your bike turns up on time, you can have a little bimble around the city; if it doesn't, you'll have a few hours to kill near Gare du Nord. I suppose you could walk up to Sacre Coeur or have a long lunch.

Have you had a look at seat61.com ? 

I travel a fair bit around Europe by train and that website has a fantastic depth of information.

I wouldn't take the box, I'd have a look on ebay/gumtree for a bike bag (or see about borrowing one I guess). It'll be a lot lot easier to move about the train.

Good on you for getting the train, its a far more civilised way of travelling. Last time I flew with the bike,  Alitalia gave my boxed bike a right going over and next time I take it anywhere in Europe it'll be by train. 

It depends where abouts in N Italy you are heading. 

There are trains from Paris Gare de Lyon to Milan.   You can also get from Paris or Brussels to Turin by train.  I suspect you will need to box up your steed for the Eurostar (if that is how you intend to get to continental Europe rather than the ferry)  and probably for the French/Belgian/Swiss/Italian bit too.

It is cheaper and quicker by plane, which is a shame.

I think there's a service that takes them from London to places in France, could you use that and then ride from there or catch a train?  

Check SNCF too, the French railway company.

We drive to the east coast of Italy every summer, takes about 20 hours driving, so Milan would be be around 13.  If there were two drivers you could just about do it without an overnight stop, but it can be knackering and it can take a lot longer if you are unlucky with accidents and or traffic.