Banff! Done Realize that crowds thin-out during weekends. If she's cool with a mountain Honeymoon, then you'll be good anywhere. Among your original 3 options, don't do Vermont. Just a totally different vibe than the Rocky/Cascade Mountains!
Be sure to check holiday schedules. There are many state-side holidays during the middle of February (Presidents/Ski Week etc.) and ski resorts can get pretty crowded. I don't know Canada's schedule, but avoid these weeks for thinner crowds and thinner prices.
Traveling the States and Taking Pictures