1) Winter getaway the hole you have to land in for the super trials achievement there is a hole next to that land in there thats squirrel number 1.
2) The Substartum stop on the platform that has A9 on it stop completely on this platform then roll of backwards fall down and thats squirrel number 2.
3) Stratosphere: when you get to the part were its zero gravity youll want to bail out up as high as you can and start floating back up backwards ( Technically opposite the green thing that you need to break to get into the zero gravity challenge) if and when you get up high enough youll land on a platform and that squirrel number 3 .
Hope this helps