If you have the budget, sure. The LT isn't terribly warm walking around town, if it's cold out. I was in Banff for a week and we got a cold snap. So cold my breath was hitting my eyelashes and freezing on impact. Walking 4 blocks, I had mini ice cubes on my eyelashes! Funny in hindsight, but crap was it cold. On the slopes it wasn't so bad because I could work up some heat lapping a few groomers.
Another day it hit 1C and I was on the patio with no hat or mitts, jacket open, and enjoy a drink in the sun. But I guess I'm used to the cold. I often go skiing at night when it's -10 to -15C consistently or worse with wind chill.
If you're not used to really cold weather, the extra layer will help. The Atom LT is an excellent mid layer, but if it's really cold out, a thin fleece underneath will work wonders. My wife is petite and not so good in the cold, that's the layer setup she uses and then she's fine for the whole day.
I wish I had an Atom SV for around town, that would have been perfect!
BTW, between Banff, Big White, and Whistler, that is one HECKUVA Canuck trip, you'll have a blast!