Specifically, I've been thinking a lot lately about a circumnavigation of Lac La Ronge. Lac La Ronge is a large lake about 380 km north of Saskatoon, straddles the edge of the Canadian Shield and is surrounded by boreal forest. The southern portion of the lake is sandy and wide open, while the northern portion is rocky and full of granite islands. It may not be "Great Lake" big, but it's still pretty darned big at approximately 35 km across from the town of La Ronge on the western shore to the eastern side, and about 65 km from a bay in the southwest to the exit of the Rapid (Montreal) River in the northwest corner. It's large enough that standing on the shore in the town of La Ronge and looking ESE to the open lake, you see nothing but horizon.
View Lac La Ronge Circumnavigation in a larger map
A circumnavigation that generally follows the shoreline but is not strict about following the bays and completely skips Hunter Bay would be over 220 km. One could cut this down somewhat with a few more shortcuts in the northern portion of the lake, but at some point you would jeopardize being able to call it a "circumnavigation". Hunter Bay is a large lake unto itself (~18km x 19km) and adding a circumnavigation of the bay adds another 68 km to the trip.
Because of the large open nature of the lake, especially in the south end, I think this trip is best suited for sea kayaks rather than canoe. If you can figure on 25km per paddling day, the trip would take about 9 days. Add on some days for rest and being windbound, and we're at about 12 days even without Hunter Bay. It seems possible to do it in less time (30 km days, for instance), but that allows less time for fishing, repairs, rest & recovery, etc. and I would be reluctant to count on it. I should be able to carry 12 days of the food in the kayak, though I will probably need to pack more lightly than I am accustomed to. There are a few points where road access is nearby and so egress in case of trouble or re-supply are both possible. Overall, much of the lake should have a fairly remote feel to it, but there may be the occasional motor boat around, especially in the northern end of the lake. Lac La Ronge is a popular fishing destination so it would have that safety net of not being completely isolated.
I don't know if a trip of this scope would ever be in the cards, but it can be fun to plan regardless. In the meantime, I will keep working on my paddling skills in order that when the opportunity to take on a challenge like this, I have the skills to allow me to do it, and to do it safely. Perhaps I should start off with a mini-expedition, such as the circumnavigation of Candle Lake.
Note: All of the above is pure speculation. I have not gone over the topographic maps in detail and have not engaged in figuring out the logistics of such a trip. Do not use the above information to plan your own trip other than as inspiration!