Nahanni River
Northwest Territories, Canada
Carve the Grand Canyon a bit deeper, plunk it down in Canada's Mackenzie Mountains, and you've pretty much got the Nahanni. The Class II-III route plunges past 5,000-foot mountains and through 4,000-foot canyons. Distance: 180 miles; 14 days Gradient: 8 feet per mile Season: June-early September; best in September Do It Yourself: Put in at Rabbitkettle Lake; take out at the Laird River. For a permit (required), call Nahanni National Park Reserve, 867-695-3151. Nahanni Wilderness Adventures (888-897-5223; www.nahanniwild .com) rents canoes for $21 per day. Guided Trips: Nahanni Wilderness Adventures runs 14-day canoe trips for $2,130 per person.

Noatak River
Northwestern Alaska
You'll likely see caribou and grizzlies—along with stranger-looking creatures like long-billed dowitchers and musk oxen—as you paddle the Class I-III Noatak from Gates of the Arctic National Park to the wetland tundra of Noatak National Preserve. Distance: 340 miles; 24 days Gradient: 13 feet per mile Season: June-early September; best in September Do It Yourself: Put in at Pingo Lake; take out at Noatak village. No permit required. Brooks Range Aviation (907-692-5444) rents canoes and rafts for $25Ð$50 per day and offers float-plane service to put-in and take-out points. Guided Trips: Equinox Wilderness Expeditions (877-615-9087) leads 24-day canoe trips for $3,600 per person.

Hayes River
Northeastern Manitoba
Think of the Hayes as a wide, meandering highway (with a few Class II-III rapids and a portage or two thrown in for good measure) through the vast boreal forest of the rocky Canadian Shield. About 50 miles before the river dumps into icy Hudson Bay, you'll start spotting playful ring seals. Distance: 225 miles; 14 days Gradient: 4.5 feet per mile Season: June-August; best in August Do It Yourself: Put in at Oxford Lake; take out at York Factory. No permit required. North River Outfitters (204-778-6979) rents canoes and kayaks for $20 per day. Guided Trips: Wilderness Spirit (204-774-2140, www.wildernessspirit.com) runs 14-day canoe trips for $2,750 per person.