City beat Chelsea 1-0 on Saturday, turning in a dominant performance at Stamford Bridge , with Kevin De Bruyne's goal enough to seal all three points.
Guardiola's men subsequently sit atop the Premier League table, level on points with United and five points above Kane's Tottenham, while Chelsea sit a point further back.
Kane was in exceptional form earlier in the day, scoring twice as Spurs thrashed Huddersfield Town 4-0 , to take his tally to 11 goals from nine games in all competitions this season .
The England striker was given a rousing ovation from both sets of supporters as he was substituted during the game, and Guardiola is wary of his prowess in front of goal.
"We’re in September. Chelsea won 13 games in a row last season. They were unbeatable, they won the league. It's not easy," he said.
"Of course this season they play in Europe. It's a little more complicated for all the teams.
"We have United [and] the Harry Kane team who scores every game two or three goals.
"Jose with United will always be tough. That is a Jose Mourinho team, aggressive winning duels and so quick on the counter attack. They are already convinced they can do it in this way. It will be tough."
Guardiola was delighted with his team's performance at Stamford Bridge, too, and he lavished praise on all of his players, after De Bruyne scooped the Man of the Match award.
"We're so happy for the victory, because we're here for the result, but especially for the way we played," said Guardiola, whose only win away from home against a top-six opponent last season came more than 12 months ago at Old Trafford.
"It's not necessary to say how good [Chelsea] are, how strong, how fast, how quick. They are able to do absolutely everything .
"We played with courage, to keep the ball, to make high pressing. To provoke what happened in the last minutes and to provoke them to play long balls through Marcos Alonso.
"We play so high. John and Nico were amazing making the line high. You know how difficult it is to do that against Alvaro Morata, Willian, [Eden] Hazard. When they receive the ball in those positions you are dead.
"Leroy, Gabriel and Raz [Sterling] made an outstanding performance. They didn’t let Chelsea have time to think or put the ball in behind.
"In the second half the impression was good. They didn't have the ball. We could retain the ball and attack and attack."
After the first trophy-less campaign of his career last time around and a busy close season reshaping his City squad at considerable expense, Guardiola was clearly delighted to have claimed a major scalp after sticking to his stylistic guns.
"You realise after 1-0 we didn't defend. We continued to play. We created enough chances to score more goals," he said, having dedicated an eighth consecutive victory in all competitions to absent injured duo Sergio Aguero and Benjamin Mendy.
"We try with Manchester City to convince the club we're able to go wherever and play our game. I'm so satisfied because we won in the way we tried from the beginning."