I don't think there's a "best" in a specific area for viewing wild life. There's more of a "luck" involved.
We had otters in several of the rivers, moose along the roads, but not in creeks or lakes, no matter how far out of the way, a playful young black bear one year at rock lake campground, who was batting a pail around, but never saw one on a trail yet. So just go out and maybe one day you will be lucky enough to see any wild life at all, because That's what keeps many of us returning to Algonquin year after year, hoping this is the year......

I agree with Shayne74 that earlier in the summer is better for wildlife than August. However I would say that if you can incorporate the Tim-Rosebary-Longbow corridor your chances will be as good as they can be... it's a well-known hotspot for moose and I've seen both moose and otters there in August.

Misty Lake and the upper Petawawa has also given me a lot of moose sightings, though I've never been there in August specifically. Other places I've seen otters include McCarthy Creek and Joe Lake. The more wetlands you incorporate into your route the higher your chances of that sort of wildlife.

Bears are more difficult to give a straight answer for. They're the least commonly seen animal of those you've mentioned, especially in Algonquin -- I think bears are a more common sighting even in some of Ontario's other wild areas. And more importantly, they don't stick to specific hotspots or habitat types the way moose and otters do. When bears do become a frequent occurrence in one place, it's usually associated with unnatural food sources. Like last year with the bad berry crop there were lots of bear sightings in and around the Highway 60 campgrounds. Backcountry bear sightings do happen but I don't think there's a particular route for it.