Niagara Falls, both the U. side and the Canadian side. Winter everything is covered with ice and snow -- and you can always find new things to see and do! It's an amazing (and VERY romantic) place to visit!
Niagara Falls is a sight to see, but located south of Seneca Lake in the Finger Lakes region lies a lesser-known fantasy-like area called Rainbow Bridge and Falls in Watkins Glen State Park, New York. Maybe on Montreal trip?