Thank you for getting back with your second question. I don't believe a worn timing chain would make a squealing noise, but a bad timing damper might. Since the timing chain and damper are easily accessible without taking the whole motor apart; it would be worthwhile to use a stethescope to determine whether the noise comes from the timing cover area. If it does; it would be worth removing the timing cover and inspecting the timing damper.
There is one other type of engine problem which can produce a squealing noise, and that is a rocker arm which is not getting lubrication. If the noise comes from the valve cover area; it is easy enough to remove the valve covers and inspect the rocker arms and their pivots. These parts can be replaced at a relatively small cost without going deeper into the motor; but if the type of wear indicates that other parts of the engine are also probably affected; I would not go deeper into the motor.
If there was a bad bearing in the engine; the cost of repairing it would be nearly as much as the cost of buying a freshly remanufactured motor, and there would still be a significant chance that other internal engine parts were also worn. So I would not recommend tearing down the engine to find and replace a bad bearing. Instead, if that was the problem, I would replace the engine with a remanufactured one. You can buy a completely remanufactured engine for that vehicle for about $1,400 from www.rockauto.com. I would also contact Hiperformer engines at the link posted below, and compare their prices and warranties. Those two places have better prices and better quality motors than you can find elsewhere. The regular Grand Prix has a 3.8 liter V-6 motor The Grand Prix GTP has a 3.8 liter supercharged motor, and the Grand Prix SE has a 3.1 liter V-6 motor. You'll need to find out which model motor is in your car; before ordering a replacement.