If you don't have to leave the international transit zone (i.e. your luggage will follow without you having to collect it in BKK and check in again), then no need any visa. Anyway, with only 1h20 min, you would not have enough time to go through immigration, collect your luggage, go through immigration again and catch your second flight. When you check i in Nepal MAKE SURE YOUR LUGGAGE FOLLOWS TILL MELBOURNE !
You are in a foreign country and your Canadian Embassy has asked you to give them your current passport and stay without it for 6 weeks before delivering you a new one ? Really ? My Swiss embassy ask me to exchange my old passport for the new one only the day once the new passport is ready ! They then make a hole in my old passport and I can even keep it if I wish. Poor Canadians...
Just keep in mind that our passport does not belong to us, but belongs to our government. There are some obligations. One of them is to not let it in the hands of non-officials, especially in a foreign state.