Easiest route to florence

There are no direct flights from US to Florence.

You can use Google Flights to check your options.

Fly to Milan or Rome, and take ground transportation from there...

Aer Lingus will sell you a ticket with connection in Dublin from Cleveland to Rome or Milan, then you can take the train.

Your best option is to fly to Rome FCO with any airline. There will be at least one layover somewhere in the US or Canada.
Then from Rome airport you go to Florence by train.

Thanks all for your suggestions.
Very helpful.
I’m actually going to montecatini terme.
Perhaps there are direct trains from rome or milan

No direct trains to Montecatini Terme from Milan or Rome
You will need to change in Florence

https://www.trenitalia.com/content/tcom/en.html

Station names:
Milano Centrale
Roma Termini
Firenze SM Novella
Montecatini Terme-Monsummano

I see that British Air runs a direct flight from Pittsburgh to Heathrow ... arriving there at around 11:00 AM local time. For our own last few trips to Europe we've opted for something similar from Denver, ie taking a direct flight to Heathrow, and then electing to spend the night at one of the reasonably priced Premier Inns that are dotted around the airport in order to get a good night's sleep in a real bed before continuing on the next morning - refreshed and ready to go.
That's how we opted to do it for an anniversary trip to Florence a few years ago and it worked out great for us. From Heathrow, BA has a number of reasonably priced options flying into either Pisa or Florence. In your particular case Pisa might be preferred - I think the flight is a little cheaper and since the train station is virtually co-located at the airport, requiring only a local people mover little tram to get from one to the other, you can quickly be on your way to Montecatini which is about an hour away.
If you don't mind the 2 hour drive to Pittsburgh that might be a viable option for you, and if you'd rather not layover at Heathrow you could just continue on upon arrival to either Pisa or Florence.

We live in Bay Village. We always drive to the Detroit airport and fly Delta nonstop to Rome…we prefer the 2 hr 15 min drive from our house to the Detroit airport more than a layover anywhere. Then you can take a train from Rome to Florence (although we always drive as we stay in either the Chianti or Val d’Orcia regions of Tuscany, not in Florence).