All persons flying into the U.S. -- even those merely transiting there -- must be "admitted" into the U.S. U.S. airports do not maintain sterile areas for transit passengers. As noted above, your pre-cleared flight will land at EWR as a "domestic" flight, as you will have cleared both Immigration and Customs in YOW.

In theory, U S. CBP could board a pre-cleared flight at its U.S. arrival airport for further inspection, but this is not likely to occur unless CBP learns something about one of the passengers after the passenger has already passed pre-clearance at the foreign airport.

Check the baggage claim check you receive at YOW, to make sure that your baggage is checked all the way through to Tahiti.