The modern, two-story building that’s been taking shape this year in a prominent, conspicuous location opposite the train station on Elm Street is set to welcome its first major tenant in the coming weeks, officials say. Stewarts Spirits, the fine wine shop added in 1974 to the New Canaan’s family’s longtime market by Robert Bailey Stewart—grandson of Walter and Nellie Stewart and son of Walter A. Stewart Sr. and Audrey Bailey Stewart—is on track to open in the brand-new structure this fall, according to Doug Stewart. “We are excited that the new home of Stewart’s Wine & Spirits is taking shape and we seem to be in the home stretch,” he said. The shop will occupy the 1,623-square-foot first floor of the building, designed by Westport-based Frederick William Hoag Architect. Melissa Engel, who owns the property and has overseen the new building’s construction as project manager, said the glass walls of the second floor space will go in this week.