Special Town Meeting voters on Sunday will be asked to decide whether to amend the zoning bylaws covering a 58-acre parcel at 129 Parker St. to accommodate a multiuse development dubbed the Shoppes at Maynard Crossing. The project, proposed by Southborough developer Capital Group Properties, would involve 250 apartment units and about 300,000 square feet of retail space. The rezoning vote requires a two-thirds majority. The meeting begins at 1 p.m. in the Fowler School. Residents will be returning to the school at 7 p.m. Monday for annual Town Meeting and another Special Town Meeting session.