Over all diameter of the 3 wheel and tire is 26.3 inches, the Y wheel and tire is 28 inches. Snow tires meant for the Y will not fit on the 3, they will hit the upper control arm of the suspension. If you get snow tires that fit the 3 they will look ridiculous on the Y, and throw off the speedometer and odometer readings by a significant amount.
Face it, if you live in an area that gets significant snow you are NOT going to be swapping the wheels and tires back and forth between the 3 and the Y on a regular basis anyway. You can either pick one to be your winter driver, or you need to get a set of snow tires for each rather than trying to share a set of snow tires between the two.
If you plan to sell the 3 after you get the Y, then get a set of snows for the 3 for this winter, and sell them when you sell the 3 and at that point get snows for the Y.
Keith