I sent the link to your photo to someone who sent your photo to someone else who... well, long story short, I've heard back from Mammalogy at the Royal Ontario Museum. They were unable to positively identify the photograph from just the single angle, but they are skeptical that this guy is a Least Weasel. They could find no record of Least Weasel in the Toronto area, although it is a surprisingly difficult animal to find in the wild. The best guess is that your photo shows a young Ermine.
I don't suppose you have any more pictures of this guy? One showing its tail, hopefully. Or, do you remember seeing if the tip of the tail was black?
P.S. Nice shots!
