Im a Canadian who was charged for dui 12 years ago. I never returned to the US in fear of going to jail. Can i cross the border now?

A DUI charge is both a civil and criminal offense.  If you did not show up in court on your appointed court date then a warrant for failure to appear would have been issued.  Warrants don't expire.  If you attempt to come back into the country it may well show up; technically it is supposed to but as a practical matter it may not (administrative error, etc).  However, you won't know this until you attempt to gain re-entry .  If it does show up you can be taken into custody.

Right now, you should contact an attorney in the area where the warrant was issued.  Have them check on all of this for you.  Until then, I would just stay put.