Cubs are simply young bears. Cubs have all the physical and mental attributes of a bear, they just aren't old enough to be a full-fledged bear.
Otters are slimmer and less hairy.
Wolves are bears that are typically more aggressive and OVERTLY masculine.
I saw five river otters in a marsh last week, they were swimming around each other, and looking like they were having a great time. Otters always look like they're having fun.
They can be surprisingly hard to see, for such large creatures. When swimming in deep(ish) water, they just poke their heads up, and if you see the head out of the corner of your eye it's surprisingly easy to mistake it for a piece of wood or a duck.