Replying to Backpack

Hello Friends,

I just found out me and my family are setting out on an excursion across the country this summer. (no not walking) We are taking the train accross canada but all we can take for luggage is a backpack. So i need a BIG pack. I want the pack after the trip to be useable on ski touring trips in the future, therefore a ski compatable pack. It needs to be around 50L (3000 cu. in.) and i would reely LOVE it if it didnt weigh more than 7 pounds. I was looking at the Dakine Guide pack and thats kinda the number one pack in my mind right now. Anyone have any other suggestions. Thanx guys.
Cheers,
-Keegan