I like the Rivendell site and think they have lots of good ideas. Unfortunately almost none of them have anything to do with the kind of trip you are proposing. They are the retro touring style company, not the expedition touring company. I wouldn't bail on the trip if I was stuck with a Rivendell, but it would not be on my wish list.
It would help to know where you are located since the cost of getting a frame varies a lot depending on where you live. It would also help to know your size. It's a lot easier to get expedition grade frames for small people. The LHT with 26" wheels seems pretty much ideal.
Sakkitt has the best concept for what you are planing, but they will never be ready unless you are leaving in about 2 years. After them maybe the Coomotion, though they are a 700c frame, however that's an option certainly. Then there is Rock and Road by Gordon. It would be a great choice. IF makes some custom bikes that seem good and not too slow to get.
If you are in Canada check out Arvon Stacey.
Cost wise, the main issue is how well you fit off the rack. If you are normally proportioned, not super long legs and short body , or the reverse, etc... then you should be able to fit a stock bike and you will not gain the main advantage of a custom bike. If you are easily fit off the rack, then 1400 dollars is cheap for what you get in a custom bike.
To check out more custom options check out the touring options here, and their framebuilders list:
http://www.sandsmachine.com/#Touring%20Bike%20Photos:
I was in Labrador one late June. Very deep snow everywhere. We were fishing, and the ice was off the rivers between the lakes so we did OK.