Santa Successor: The new Santa should be...Lucy!
From the moment Scott mentions looking for a successor, my mind has squarely been set on Lucy Miller as the top choice.
We already know Charlie isn't interested, and Cal is going to be focusing on being a young adult in College. Sandra didn't seem overly interested either and the end of Season 2, it seems as if her focus will be on learning more from La Befana and perhaps that will lead to her becoming more of a guardian to the North Pole (and perhaps the entire Legendary Figure world...spinoffs anyone?).
(Side note: Did it bother anyone else that Scott mentioned Charlie but not Neil, Laura, or Lucy as someone for Sandra to focus on the Merry things in her life as she was trying to change Cal back? Are they trying to erase that huge part of Scott's family for some reason?)
Lucy may not be Scott's daughter by blood, but we saw that he always treated her as if she were his own daughter, even setting aside time to have special one on one Lucy/"Uncle Scott" moments, such as when they would play go fish and have hot chocolate, or when he was showing her his snow globe connection and they bonded over their shared fondness for them.
Lucy also has magic of her own that is seemingly separate from Santa magic, and she used it to save her parents and Jack Frost in Santa Clause 3. Where did her magic come from? Is there a La Befana connection? Are her warm hugs the extent of it or has she developed other skills? I think we absolutely need to explore that.
It also fits the narrative they've been following through the first two seasons. If Lucy takes over, Scott gets to keep the North Pole in his extended family as he's been trying to do, while the series also gets a breath of fresh air and storytelling with the opportunity to explore what being the first female Santa means.
It also never made sense to me that anyone would want a teenager preparing to take on the role of Santa. The person taking over the role of Santa should, like Scott was, be an adult with a career (that they are okay with giving up in the end) and very experienced with how the human world works. It's why the elves have Kribble Krabble for the Head Elf, despite the fact many apparently don't return.
Liliana Mumy is still in the acting world, although she has mostly done voice acting in recent years. I think she could be persuaded to return since the series wouldn't necessarily be a huge time commitment at six episodes per season. She just gave birth to her son, but we know productions work with actors so that their young children can be close to them on set. Perhaps Liliana's husband and son could even have a cameo on screen!
If she wants to limit her initial re-appearance to spend more time with her new family, it's doable. She could appear in the back half of Season 3 (along with Neil and Laura of course!) as the key to solving whatever threat is looming before Scott realizes she's who he has been looking for all this time. The final two episodes would be Lucy (and her parents) struggling with the idea before the season wraps with Lucy saving the North Pole and agreeing to take over, followed by Scott and Lucy doing the Christmas Eve rounds together (Scott for the final time, Lucy for the first time). It COULD serve as a series finale if needed.
Ideally, Liliana would return to star in Season 4 (which would probably be the final season) to fully flesh out and explore the ramifications of her taking over the role and then going through her own "Mr. / Mrs. Clause" romantic situation...or perhaps she already has a spouse, and that could be a whole thing to explore...would they automatically become the new Mr. / Mrs. Claus when Lucy takes the mantle? Tim Allen, along with a number of previous cast members could make return appearances to give advice.
I would especially like to see Curtis again as Lucy seemed to have a fun potential connection with him in Santa Clause 2. Since he gave up his immortality like Bernard, he could even be a potential love interest for Lucy if she isn't already married and they want to potentially explore that idea. I know Spencer is more or less out of the acting world these days but considering it would be the final bow for The Santa Clause, perhaps he could be persuaded to return.
Season 4 could be an extended season to allow for enough time to do a proper wrap up...maybe 8-10 episodes instead of 6.
Anyway, it probably won't happen but hey...one can always hope! :)