Because the Biergarten opens to day guests at 11am with the rest of World Showcase, it would not be available for a 3- or 4-hour reception following a 9am Epcot wedding. The only restaurant in WS that is available for wedding receptions is Monsieur Paul, which doesn't open to day guests until dinner.
However, you might try asking whether you could have your ceremony inside the restaurant instead of in the courtyard, maybe even at 8am instead of 9. I have a feeling that park management will say that opening preparations and the arrangement of tables and chairs inside will preclude this too, but at least it's slightly more possible than a reception.