Coming from the region, I can tell you exactly how it is. May and June, don't worry about bugs, but July and August are pretty 'busy' months... hehe. Still, it'd be worse if the courses were held around Valcartier. North of the St.-Lawrence river, bugs are really bad.
Year to year it can vary, but the temperature is mild in May. We had hot May (around 25-27C) and cold June (around 20-24C), but normally June is hotter than May. It's always between 22 and 28C during the day, in May at night it's 13 to 19C, during June 16 in the worst cases and 20C. July is the hottest month, nights not below 19C and day reaching peaks of 32-33 several times in the month, but between 24 and 28C normally. August can be cold at night, like May. But we had hot August in the last couple of years, which looked more like July during the day (15-18C at night) and September like a normal August, between 20-23C during the day and 12-16C at night.
Still what affects the felt temperature is the humidity. May and June tend to be drier than July and August. For example, the worst case is a 28-32C and with a lot of humidity its like a 35-39C as felt temperature, really hard. An advice, never stop drinking when its hot, humid or not.
Cheers,