Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Montreal to Klagenfurt as you normally would.
Yes, there are multiple flights from Montreal to Klagenfurt for under C$ 1,277. The cheapest flight booked recently is on Lufthansa for just C$ 1,177, but on average you can expect to pay C$ 1,355.
There are no direct flights from Montreal to Klagenfurt, but Cheapflights can provide you with all the information you need to find the fastest route with the fewest stops.
You can imagine temperatures to be in the 27 °C range in July. The weather in Klagenfurt is generally colder than Montreal's. As flight availability is subject to become more limited as peak season approaches it is ideal to book in a timely manner.
Lufthansa and Air Canada can get you from Montreal to Klagenfurt in just under 9h 55m. Your travel time can differ by up to 4h 45m. Both multi-stop and direct flights can be found to your destination and back.
Cheapflights users have booked flights from Montreal to Klagenfurt round-trip from C$ 1,178. Another airline that can offer you cheap pricing is Air Canada.