Not sure where you are in Ontario, we are in the southwest area, but still on the fringe of the "snow belt". We do get some snow here but we haven't covered any RV's we've had (starting in the 1980's) and haven't had a problem with snow load on the roof.
We are fortunate in that we now winter in the southwest US and haven't had snow (except for in Tuscon in March of 2013!).
2013 Redwood 36RL, 2011 F-450, Sat Internet, Sat TV