There are a couple of Three Mile Lakes within Muskoka....the one I'm familiar with, close to Raymond, Utterson, Windermere, is known for walleye, but definitely doesn't have herring.
Ice fishing is slow, but you can usually run into some good sized perch and the odd walleye. There is a cottage rental outfit that puts huts out in the winter, and at the deeper end of the lake there are usually a few huts out, anywhere between "Wonder Beach" and what I believe is Bathayalcock Island.
Keep one line down with a minnow on bottom and another tied in 3 or 4 feet above it, and jig another line aggressively close by. There isn't a TON of structure in the lake, aside from weeds weeds weeds. And Lew's tackle collection.
Good luck
Of course, you're not far from Lake Rosseau....you will likely be able to get on the ice in Windermere Bay and try for a few lakers