Hi, I'm not sure about this! On the west side of Sherbrooke Street, the infrastructure not suggest any crossing possibility (https://www.mapillary.com/app/?pKey=772056961680333&focus=photo&lat=45.5497828&lng=-73.5549653&z=17&x=0.7674922681836277&y=0.5320188070610106&zoom=0.6289308176100629)
So yes, this is (maybe) legally possible, but unmarked crossing tag is, I quote, "used for pedestrian crossings without zebra crossing or traffic signals. By a structural measure the transition should be recognizable." 
https://wiki.openstreetmap.org/wiki/Tag:crossing%3Dunmarked