You can hear those things miles away. The last thing I want to hear in Quetico (or any other backcountry area) is someone else across the lake honking their vuvuzela at everything they think might be a bear.

Air horns are illegal in a lot of wilderness areas too, for exactly this reason

Don't even think about taking an air horn. If you're concerned about bears, read up on bear safety precautions, keep a spotless, odourless camp, and your chances of an adverse bear encounter will be miniscule.