Two of the lenses I would consider would be either the EF-S 15-85mm f/3.5-5.6 IS or the EF 24-105mm f/4L IS. The 15-85 is lighter and covers a wide range of focal lengths. The 24-105 is built like a tank and covers a range of longer focal lengths. If you intend on taking mostly long range pictures, the EF 70-200mm f/4L IS is the way to go, but it is a little heavier and bulkier than either of the other two lenses. All three have IS and will allow you to handhold shots at lower shutter speeds when your subject isn't moving. IS will be especially useful since you probably won't have the luxury of a tripod. There are some monopods that can double as hiking sticks, and some of the higher end ones made from carbon fiber might be a consideration instead of a standard hiking stick. You might could lash it together with other walking sticks for a tripod in a pinch.

Since I'm assuming you'll be in a lot of snow, at a minimum you need a polarizer filter. Not only will it increase contrast and color saturation of a clear sky, but it will reduce the glare from reflected sunlight off the snow. Most polarizers also reduce exposure by around 2 stops but it wouldn't hurt to also carry a Neutral Density filter in the ND3 to ND5 range to stack on the polarizer when the sun is shining brightly on the snow. Remember to overexpose by 1-1 2/3 stops or so or the white snow will appear gray in your photos.