the river otters in Canada are pretty much the same as the ones we see all over in the us so technically since they are quite common, they would not be considered endangered.
Yes, the river otter is endangered for a few reasons: many because of water pollution and oil spills (it damages their fur) and hunting. They were hunted for their fur which is very valuable.
go to this link...it has great information on the River Otter. Based on what I read there, I would have to say "yes, there are River Otters in the Atlantic Region of Canada" - if you look at the map...