The attacking midfielder is being linked with a host of Premier League clubs this summer.
Given he is refusing to renew his deal at Chelsea, Mount will be sold this summer while he still has a year left on his contract.
Keane stated on TV over the weekend: "Listen, they're going to be linked with lots of players but the one that would excite you really is Kane.
"He's [Mount] just gone off the boil a little bit. He can bounce back and he's got quality, I was raving about him a few years ago but he's just gone missing the last year or two.
"Again, one or two injuries and the fact he can't get in the Chelsea team I wouldn't be hanging my hat too much on him to improve United and close the gap.
"I think he's a good player but would he improve Man United? I'm not so sure. I think Rice would, Rice would be a decent signing, but in terms of the excitement and goalscoring, I'd go all-in for Kane. But, can I see Spurs selling to Man United? Very, very difficult."