I come from the North-- The best advice for blackfly seasons is to stay the hell away. I'd actually call ahead and ask, as the blackfly season is fairly short, but varies by location. Your best hope is a strong wind or a moving boat if they're out. There's nothing like a constant swarm of small biting critters.
For mosquitoes or misquotes you can use a spray (which is the only way to get your hair and clothing) or some rub on stuff (some of the newer ones are more like lotion), but citronella candles are nice(r) if you're in a fixed location, IMHO. If you don't mind toxic smoke the oldschool off 'pics' work well-- particularly indoors or in a tent. The same will work on blackflies, except they swarm worse, and will swarm during midday until you have a hot spell. Mosquitoes mostly stick to the shade, dawn, dusk, and the early dark. Then there are only the 'horse and deer' flies to worry about.
I just went home for a family thing and god the blackflies were bad, but the mosquitoes weren't really out yet. But that was wayyy North. I love Toronto.