Yes, the Jean-Bentpine loop is a good one.

When I did it in July '04, the only real solitude was the stretch from Bentpine Creek through Sturgeon. Still "busy" by Q standards isn't that busy at all. A very scenic route.

The Cirrus suggestion is also good. In August '06, I think I saw one other canoe for the length of the north shore of that lake. The Lerome entry does force you to go through a couple of powerboat-infested lakes to get to the park, so an alternative is to go into Cirrus via Beaverhouse (Entry point 31). But that's close to 1.5 hours drive from Atikokan. If you like big lakes, I'd suggest Cirrus, if you prefer smaller lakes, then Jean-Bentpine.

A third alternative might be to go in via Baptism Creek. That area is supposed to see little traffic, but I have no personal experience to offer here.

A good book for route planning is Robert Beymer's "A Paddler's Guide to Quetico Provincial Park". It list all of the above routes plus others. It is no so good on the side trips, but I suspect that any dead-end lake that is reasonably far from the entry stations will offer solitude.