How does it perform on winter highways

The Corolla iM should perform as well as every other FWD car that has similar ground clearance. How much grip you have in the snow depends on whether you have snow tires or not. You should definitely have snow tires since it snows for 6 months where you live. A Subaru Crosstrek with snow tires would be a much better alternative. You should also take a look at the new Hyundai Kona, though reliability is unknown and it is the first model year. If you are buying new and decide on the Corolla iM, test drive the new Corolla Hatchback because everyone is saying the new hatch is a lot better than the older iM. For ground clearance and standard AWD, the Subaru Crosstrek would be a better fit.

Agree with Lectrofuel - have little to add. Snow tires are the driver here although if you have to climb 15-20% hills, I have found in snow the FWD cars with snow tires I have owned cannot make it up the hill I live on (owned both FWD Toyotas and Hondas and neither in the snow made it home even with snow tires, however a Saab I owned was slightly better and with a mighty struggle could make it up the mountain). I moved to AWD on one car in 2013 and the other this April when a tree killed my FWD Saab.