Western Uplands is an overnight backpacking trail with loops of 32 - 88 kilometres in length. The trail can be accessed from the Western Uplands Backpacking Trailhead/Oxtongue River Picnic Ground or the Rain Lake Access Point.
The loops of this trail are described here: https://niackery.com/journiackery/local-trails-travel-tips/popular-routes-uplands-trail-algonquin-park/
The GPS track on the map on this page shows Loops #1 & #2, with Loop #1 nested in the larger Loop #2. Loop #3 is listed as 88km, but that includes an out & back to Rain Lake which isn't part of the FKT route (the true loop), which is 72km.
A 4th Variation is point-to-point from Rain Lake to Highway 60, about a marathon distance (as per Lowell Greib's Strava Track).