Can answer the 2nd part but not the 1st. Shearer was definitely world class. In fact he's the best English number 9 I've seen in my lifetime (watching football for about 25 years). Like Kane, didn't have express pace. But could bang them in with either foot from 25+ yards out, excellent in the air, great touch, could score all kinds of goals, had a very good cross on him and could bring other players into play around him.
On Kane, I haven't seen much of him but have only really seen him in United games. In those games, he's done precisely nothing until he scored with that instinctive finish in the most recent dead rubber game at WHL. So I'm not that excited or impressed by him for that reason. In fact, for most of the games he's played against us he's been outright bad. I'm sure had I seen more of him I'd be more excited about any prospect of United getting him, of which there probably isn't much in the near future.