Can I leave a fresh turkey in the fridge starting Wednesday, then brine it for 2 days (Saturday and Sunday) and cook it up for Thanksgiving on Monday?
Should be okay. I'd keep it in the coldest part of your fridge and try not to open the door any more than you absolutely have to.
Besides what June said, if it's vacuum wrapped, don't open it until Saturday. That method keeps them fresh for a long time.
I think two days is much too long for a brine. Unless your brining recipe and brine specifically calls for that long, don't do it; I did one time thinking 'hey...more better' turned out to be a salt lick.
I would go for three days just to be safe ,of course it all depends on the size of the bird. It is very important to keep the brine temp at38-40 degrees. If you need a recipe for a brine,I suggest going to amazing ribs.com and checking their site it is a great reference point.
I'm with Sam, unless it is a gigantic bird, I would brine 1 day. That said, I HAVE brined a gigantic bird, so made a very intense (double strength apple cider and spices) brine mixture, put it in a large ice chest with the bird and filled the rest of the way with ice. Big rocks on top to keep any critters from having a look. I did that Tuesday night and roasted Thursday morning for Thanksgiving. It was a 25 pound bird, and there was still some ice when I took it out of the brine so it was cold the whole time.