The pair started Wednesday’s Carabao Cup win over Preston and impressed.
Garcia, 18, made three appearances in last season's Carabao Cup, before making his Premier League debut last week as a substitute in the win over Watford.
And Harwood-Bellis, a 17-year-old product of City academy system, impressed on the Asia Tour this summer, emerging now as a player capable of supplementing the senior stars.
Guardiola says both players have the qualities and mentality to be part of the City first-team picture more regularly.
“I knew they were ready," he said. "I did not need to see Preston.
"They will make mistakes, but of course they are ready. If not, they would not play with us.”
Meanwhile, Guardiola has praised Gabriel Jesus’ attitude after an interview emerged in which the striker suggested he wants to play more.
Speaking to Esporte Interativo in his homeland, Jesus praised Sergio Aguero and said he respects Guardiola’s team selections - but admitted he would love to be starting more matches.
Guardiola described Jesus’ words as “perfect” and says it’s perfectly normal for him to want more involvement.
“I read the interview and it is perfect, incredible respect like Gabriel always has,” he said.
“He wants to play, of course, he is No. 9 for Brazil.
“He is perhaps the only player with this personality, friendship with players. Every time he plays, he does his best.
“I understand completely - not just Gabriel, all the players want to play the games. It’s normal.”
City travel to Everton on Saturday as our bid to win a third Premier League title in succession continues.
Marco Silva’s side were active again in the summer transfer window, bringing in seven new players, and are widely seen as a side capable of challenging the established top six.
Last season, City struggled in the same fixture, prevailing 2-0 after a hard-fought game.
Guardiola believes a trip to Goodison Park is one of the most difficult assignments in the English football calendar but insists his players are aware of the challenge they face.
“They remain an incredible team,” he said. “They invest quite good last season and this.
“Goodison Park always one of the toughest games, and we know it. We have already prepared.
“The players know how difficult it is.”
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