Dave's point is well-taken.
Just try to locate your steps away from the various cuts, equipment, and seams in the roof (like the A/C, vents, etc.) and avoid unnecessary trips up there and you should be fine. Distributing your weight on all fours is not a bad concept, either. However, I'm about your size and went up and walked around on my roof twice for inspections and/or maintenance purposes this year (always moving about cautiously and without excess...no jumping up and down) and sensed no apparent issues or stresses.
Do they sell rubber-soled snowshoes up there in Canada?
2013 Windjammer 3008W
2006 Chevy Silverado 2500HD 6.0L w/Equalizer 4
Nights camped: 2012 (29); 2013 (26); 2014 (40); 2015 (43); 2016 (35)