City have not beaten United in the league in the last four meetings, with their last top-flight win against Solskjaer's side coming in April 2019.
"Congratulations to United for winning these duels against us, or some of them," said Guardiola, whose side were beaten by Crystal Palace in their most recent league outing.
"They have a lot of physicality, a lot of talent and people up front with the ability to win games by themselves.
"It's Manchester United - what should I say? Since the last century they have always been a good team, with the quality. But it is a new season, new games."
City were linked with a move for Ronaldo in the summer before he joined United and Guardiola added: "Normally I don't talk about players for other clubs.
"I am pretty sure Cristiano Ronaldo is happy at Manchester United and United are happy to have him. That's all."
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