Stella hopes that Norris and new arrival Daniel Ricciardo will also form a fruitful partnership, although he says inevitably it won't be the same and will need to be managed differently.
Sainz and Norris were team mates for two seasons in 2018 and 2019, and they quickly formed a bond, despite a difference in age and experience. They helped the Woking team move up from sixth to fourth and then third in the constructors' championship.
"Carlos and Lando have been excellent this year," said Stella in a team website Q&A. "The level of collaboration between the two of them has been incredibly high.
"It's one of the reasons they are so evenly matched on track. When there is an open and transparent dialogue between team mates, it elevates their performance because they can crosscheck with each other and quickly identify the weak points of the car or find the best approach to a corner.
"This has been possible due to the personal qualities of Carlos and Lando, and, I hope, the environment we have built within the team which encourages openness and trust.
"It means the drivers feel comfortable opening their box of secrets, rather than keeping that box closed so as not to give away any advantage to their teammate."
Expanding on the likely impact of Ricciardo Stella said: "He's proven that he's one of the best out there.
"The most important thing from my point of view is that we preserve the conditions that we created to allow that high level of collaboration between Carlos and Lando.
"But it's not just about preserving those conditions, we may have to adapt them. Daniel is not Carlos and his relationship with Lando will be different.
"It may be similar, but it will not be the same and we need to be mindful of that and adapt with a view to maintain the standards."
McLaren technical director James Key expects Ricciardo to be a much stronger package than when they worked at Toro Rosso in the early days of the Australian's F1 career.
"He's an excellent driver to work with," said Key. "He will have accumulated plenty of experience and knowledge since I last worked with him, so I expect he'll be several steps ahead of where he was back then in terms of what he'll bring to the team.
"He arrives as a proven race winner and is someone who can go toe-to-toe with the very best drivers. Daniel is very easy to get on with, but he's hugely determined and that has a positive effect on any team.
"He will be a great reference point for us and, together with Lando, we will have one of the strongest driver pairings in the paddock."