I am in the US on a B2 visa and my stay expires on August 30. I have filed an I-539 (extension of stay) and the status is pending. Will I be able to travel from the US to Canada after August 30 and enter back to the US with the pending I539 document?
USCIS Nonimmigrant Services (page 6)
What if I file on time for an extension, but I leave the U.S. before USCIS makes a decision on my application?
If you leave the U.S. before a decision is made on your application to extend and you plan to return to the U.S. in the future, please keep a copy of your application plus the receipt notice to show to the Immigration Inspector on your return travel to the U.S. Otherwise, you may be denied entry for overstaying on your last visit.