Is the steel cylinder by the alternator the tensioner? I was wondering if this thing rotates or not? The belt looks like it was rubbing against this hard before it failed.

How hard would it be to replace this and what exactly could've caused the failure?

 

I'm not 100% certain what part you are referring to, but tension on the alternator belt is adjusted at the alternator. there is an adjustment bolt just under that alternator. If I remember correctly, it is a 12mm bolt

 

This is on a v6 model, probably different from the 4 cylinder model. Figured out that the tensioner pulley seized which caused the belt failure, but how do I get this pulley out?

The bolt that attaches the pulley is too long to take out, so had to take out the whole tensioner assembly. I've already removed the top and bottom screw, but it wouldn't come out. Any help please!