What is the ruling on combining the Maghrib and Isha prayers without shortening them, due to the long daytime in Canada, and the questioner's desire to sleep early in order to wake up for Fajr prayer?

It is not permissible to combine two prayers for the purpose of waking up for Fajr prayer, as this is not one of the excuses that permit combining prayers. Rather, each prayer must be performed at its appointed time, while taking the necessary means to wake up. If one is overcome by sleep, there is no sin, and one should pray Fajr upon waking.