Sancho has been United's top priority and although they have been frustrated with Dortmund's negotiations, sources have told ESPN they have not given up on signing him before the transfer window closes on Monday.
"Jadon Sancho is a top player, but I find it odd that he has been Manchester United's transfer priority," he wrote in his Sunday Times column.
"Why consider paying close to £100 million for someone similar to talent you've got already? United have Marcus Rashford and Anthony Martial and where would Sancho's arrival leave Mason Greenwood, who plays in the same position and is of similar age?
"I'd rather put that £100m towards trying to get Harry Kane. Yes, getting Kane out of Tottenham would be difficult, maybe impossible, but United are a club who should always make an effort to sign the very best players and Kane is exactly what Ole Gunnar Solskjaer needs, as is Erling Haaland, who United missed out on last year -- a genuine No. 9.
"There are not many who fit that profile and are of elite standard in football right now -- yet the chances of United developing into a title-challenging team would be greater if they had such a player.
"A Kane or Haaland or someone like Robert Lewandowski would give Rashford and Martial someone to play off and freedom to roam into different areas, pick the ball up and try to beat men -- without the burden of always having to score."
Cavani is set to become the club's second arrival after midfielder Donny van de Beek.