Welcome to having a toddler. It's a lot of fun, but it does come with certain ... complications. This is one of them, and it happens for pretty much everyone.
First: this is, to some extent, a phase. He's now able to move around and do things he wasn't able to before; so he's exploring that new freedom, and all of the stuff that comes with it. Be prepared to deal with some days where he's tired because he played way too late the night before; hopefully, in time, it'll stop being quite so new, and the allure of sleep will return.
Second: this is, to some extent, not a phase. This is something that some kids in particular, but in general all kids, can struggle with from time to time: properly regulating sleep versus the excitement of not-sleep activities. For some this doesn't go away ever - even in adulthood it's very hard to properly manage sleep for some. In particular, it's important to recognize if your child's preferred sleep time is different from what you'd prefer, and be prepared to work with that; for some people, sleep at 8pm wake at 6am just doesn't jive with their internal chronometer, and so it's hard to sleep at 8pm.
What worked for us with our children, one of whom falls into the first category and one who falls into the second catergory:
- Remove the distractions, as much as possible, and take it super slow moving into bedtime. It sounds like you're already doing that, so, great!
- Don't try to remove all distractions though: give him one thing that he can have. For us at that age, it was an mp3 player (not a phone or a screen, something that only played music), which allowed our child to play some classical type music (or Thomas the Train or similar) under his control. This helped develop good habits, to some extent, and meant we weren't leaving him to be 100% bored in bed.
- Adjust the sleep time back some, if it's appropriate for your child. It's not always possible, but if he's tired at 9pm, maybe start bedtime at 8pm instead of 7pm. That way he's closer to being tired, and less likely to get worked up which might delay bedtime further. Our oldest goes to bed at 8:30-9pm now (8yo), and has since he was 4; if we try to make it earlier, it backfires, consistently.
- Tolerate the waking up for as long as it's not impacting him physically. You'll know when he's not getting enough sleep - it's quite obvious - though if he's down below what you're comfortable with, bring in your pediatrician and check with them for what you can do to monitor the sleep levels. We did that, and the pediatrician gave us some things to look for - mostly, falling asleep during the day (on car trips, etc.) excessively, and excessive moodiness (though with a 3 year old, that's sort of hard to differentiate from just normal age appropriate behavior). Our youngest had a few weeks of exploration before they settled back down; didn't work so well with our oldest, as he's definitely a late sleeper like I was, but worked for one kid. But overall, the child will have to learn for himself how to settle and how to go to sleep with this newly active brain of his; letting him work it out now is important.
- Do give him tools to help him figure out how to sleep. Talk to him gently when he's clearly struggling to go to sleep. Give him strategies he can use. "I notice you're having trouble going to sleep. It's really important to get enough sleep so tomorrow we can have a good day! Maybe you can try thinking up a story in your head. We can do that together tonight, what do you think?" Then do so - make up a story that will make sense to him. For us, we made up Curious George stories, as he enjoyed that book and it is extremely formulaic ("This is George. He is a good little monkey, and always very curious." Then he goes and explores some new thing. Then he gets in trouble because of his curiosity. Then something else happens that it turns out to be useful that the trouble happened - like finding a lost kid in a supermarket, after George wandered off - then he is reunited with his "parent" (The Man With the Yellow Hat) and all is better.) We'd do that together sometimes, and then later they got good at doing it for themselves. Not always effective, but one strategy; come up with others, too, perhaps ones that work well for you when you need to get to sleep.
Just remember this isn't something unique to you; everyone goes through this, and everyone gets through it at the end. It'll be trying at times, but the flip side is that your toddler is learning and expanding his mind, which is exactly what he should be doing at this age!