Hi I'm putting in a 200 amp meter on my barn. I also am putting a 100 amp service panel inside I was wondering if I can use a #2 aluminum for my service entrance. Lowe's sell this as service entrance and I was just wondering if I was right by doing this. Thanks for any help.

I live in copper area(no aluminum)
I would use 2- 2/0 and 1 1/0 copper for riser, If it is short run, Maybe install 200 Amp Panel. It doesn't get any cheaper or easier than now.
I would pull #4 for ground.

Underground service or overhead?
Distance of run?
When you say barn, are you planning to have live stock?
What are your plans for this barn?
To add, it's best to get info from your serving utility. Some POCO's do not allow two services on one property.

To answer your specific question, yes # 2 aluminum is allowed for a 100 amp service entrance to the house panel, fed off the 200 amp panel in the barn.