Joey,
Excellent choice in hiking destination. Glacier is the most beautiful spot in the world, but I'm probably a bit biased.
Twenty miles a day is possible in GNP and would probably require you to do around 2500 vert. The problem with that distance however lies in campsite spacing. You will need to research the distances between campsites and plan that into your itinerary.
The very same questions you posted in this thread have come up a number of times here on BPL and I receive this question in my email inbox about once a year so I've come up with a canned response that I will post below. It may or may not answer your needs specifically but it's the advice I choose to give. Note the days/mileages will obviously change if you up your mileage to 20 mi/day. You will walk up to across and over the most beautiful country if you do big miles like that so you may wish to minimize your mileage between camps and then expend your energy climbing peaks while at camp as opposed to doing big miles on trail. I HIGHLY recommend this option.
— — —
Trip One – "The Northern Traverse" – 7 days, 6 nights
This trip consists of 7 – 10 +/- mile days and will allow participants
to experience the entire Northern span of the park. It brings you up
and over both the grueling Stoney Indian Pass as well as the mellower
Brown Pass (the continental divide). As a means of reference as to
the difficulty of this route, I did this route in three days and two
nights last summer, averaging 20+ miles per day. It recommended as a
5+ day hike, so to do it in 7 would allow time to appreciate the
scenery and relax in camp.
Day 1. Hike from Chief Mtn. Ranger Station (Northeastern corner of
the park) to either Cosley or Glenn's Lake campsite
Day 2. Hike to the gorgeous Stoney Indian Pass campsite
Day 3. Hike to the Goat Haunt area (can't remember the names of camps here).
Day 4. Hike to the Lake Francis campground which is in my opinion the
first or second best campsite in the park.
Day 5. From Lake Francis, climb the mellow Brown's Pass switchbacks,
and head to either Hole-in-the-Wall or Boulder Pass campsites.
Boulder Pass is the other "best" campsite in Glacier. Even the toilet
(an open air "low-rider") provides a spectacular view of the Whitefish
Mtn. Range.
Day 6. Drop down the pounding switchbacks to either the camps at
Upper or Lower Kintla Lake.
Day 7. Finish the trip by hiking out to the Kintla Car camping area.
— — —
Trip Two – "Coal/Nyack Loop" – 6 days, 5 nights
This is considered the ruggedest route in Glacier in that it
encompasses many (low water depth) stream-crossings and is in the
remotest section and least visited part of the park. The trip begins
and ends with a ford of the Middle Fork of the Flathead River and
begins and ends with forested walking. The middle days of the trip
are filled with expansive views of high peaks and passes as seen
through the remains of the all-encompassing fires of 2003. The trip
stays to the valley floor except for one almost imperceptible crossing
of Suprise Pass.
Day 1 – Begin at the Coal Creek Trailhead (get precise directions from
a ranger or use the Shuttle Service), ford the Middle Fork and hike
approx. 6 miles the Lower Coal campsite.
Day 2 – Hike another 7 to 10 miles through trees and one or two fords
to Upper Coal creek campsite.
Day 3 – From Upper Coal you'll head into the burn of 2003 which allows
amazing views of the surrounding peaks and in particular, Mt. St. Nick
(a Matterhorn-ish looking peak) until you come to the Martha's Basin
area. The campground is at Beaver Woman Lake and this hike is approx.
10 miles.
Day 4 – Cross the easy Suprise Pass and continue hiking through the
burn until you arrive at the Upper Nyack campsite.
Day 5 – Hike to the Lower Nyack campsite.
Day 6 – Return to the trees and hike out, fording the Middle Fork
again and once again entering civilization.
— — —
Trip Three – "Dawson/Pitamakin Pass Loop" –
This is a very short trip that many people do as a long day-hike. It
starts and ends from the Two Medicine area of the park and one can
actually catch a scenic boat ride rather than hike the first half of
the first day.
Day 1 – Hike/ride the boat along Two Medicine lake and then ascend to
the No Name Lake camsite.
Day 2 – Climb Dawson pass and proceed along a ridge and sidehill to
Pitamakin Pass and then descend to the Old Man Lake campsite.
Day 3 – Hike back out to the Two Medicine Area
— — —
These are rough descriptions of three routes. I highly suggest
cross-referencing the routes I described with both a park map as well
as a guidebook (if you have one). I only had my memory and a topo map
to create those scenarios so I don't remember that many mileage
figures. I haven't hiked the Dawson/Pitamakin Loop in its entirety
but I've done the other two routes (the Coal/Nyack loop I've done
three times). Like I mentioned before, feel free to nit pick with
questions, as you may be able to tell from the lenght of this message,
that I don't mind helping out.