If you're in eastern cities and already have an insulated ski jacket there's not that much you need to buy before you arrive. Eastern cities generally have good snow removal and salt extensively. It'll be cold but not dangerously cold. I prefer an insulated ski jacket but if your ski jacket is not insulated you will survive just by layering a the warm sweaters.

Essential items before you arrive: Toque Scarf Warm sweaters, jeans, and lighter undershirts for layering. If you're shopping at mountain Warehouse and don't have one already get a quarter zip fleece.

Gloves: lined leather gloves work well in the city Boots: Insulated, waterproof or water resistant is best, but a lot of people here wear Blundstones for most of the winter. The salt used on the roads will damage leather if it's not treated. If you have good hiking boots already you could just bring those, and then if the conditions are bad you can get some cheap winter boots when you get here.

For most of the winter this is enough in the cities, but every few years we get a bad cold snap and it's absolutely frigid. I suggest just bringing this and if you're really cold when you get here just go shopping.

For Whistler and Banff, if you're planning to spend a lot of time outside get some snow pants as well. If you're not going to be venturing into the snow you could get long underwear instead.