this what I did, when I lodged my TRV online application, I stated in my letter that I will be visiting friends in Toronto but I did not presented any invitation letter. Instead, I listed down an itinerary of common tourist spots around Toronto. Since I was not staying with my friends, I wrote down the hostel name, address and contact with no booking reference.
of note, I indicated that I will only be visiting Toronto from US as a short trip.
Glad I was successful on this application and given multiple TRV until passport expiration (2016)