1 day early flight thru cruiseline?

Yep.  I would say more often than not, cruisers like to arrive a day early to avoid missing their cruise due to travel delays.  And you can arrive a week early, and depart a week after the cruise if you want, you can still book through the cruise line.  

I have used both cruise line air and Expedia.  It depends on the price, and the likelihood that the cruise will be cancelled.  If the rates are the same as Expedia, I'll book air with the cruise line.  If it's a fair bit cheaper to book through Expedia, I'll do that.  

And one of the benefits of booking through the cruise line is that you don't have to pay for air until final payment on the cruise is due.  That way, if the cruise is cancelled, the air is automatically cancelled too, which is convenient, and you don't have to worry about a refund as you would if you book through a regular travel site like expedia.