Hi,
My now 3-year old son started off sleeping in his own room at 22 months but still to this day comes in at 5-6am and dozes until we all get up. It is more disruptive than I would prefer, but it is part of a gradual bed-weaning process that is as child-respectful as we can manage.
We had been spending way too much time helping him fall asleep in his bed. We realized that he was willfully staying awake and it was getting later and later. Whether to go to sleep and where to go to sleep is his conscious choice. We had to find a way that he wanted what we wanted. Finally my husband and I sat down with him and had a conversation about how tired we were of waiting for him to fall asleep and how frustrating it was for us that he was trying to stay awake when he knows that sleep is so important for helping him grow bigger and stronger and feeling happy. Our son recognized the pattern of less sleep = cranky mornings. We told him that it was his decision about where and when to sleep but that we would only help him when he decided that he was "ready" to sleep (in his bed).
What is working really great right now is a sticker chart where my son works towards the toy of his dreams. He gets a sticker in the morning if he has cooperated and helped with his bedtime routine, and gone to sleep right to sleep after story time and parent departure. The chart is posted right in his room as a reminder. It has worked like magic every night and my husband and I are amazed that something so simple could be so effective. Our hope is that once he is in a habit of going to sleep on his own, in his room, we will be able to forego the sticker chart.
I think the sticker chart only works for children that have strong wills and deep desires. It seems at this age if a child feels in control, then their decision more readily aligns with what the parents want. My son decided he wanted that toy and would do what it takes to get it. The daily toy/surprise tactic could get old too quickly. It's the working toward something that my son responds to.
Also, another thing that has worked is to make sure there is something that he loves to cuddle and help him feel safe. Because my son and I had a long nursing/weaning process, he really depends on my physical closeness to feel comfortable enough to fall asleep. I have substituted a rubber hot water bottle, the "hot water boobie" that he loves.
Lastly, when you talk to your son, you may want to ask him directly how he thinks it could work to sleep in his own bed. You may be able to surface any fears he has and work together on problem-solving around those fears. Three year-olds seem to have a lot of ideas about how to solve their problems! Try to follow his suggestions, if they are realistic. But be upfront that you will follow his suggestions ONLY if he decides to go to sleep in his bed. You can offer concessions to sweeten the pot, for example, "you may come to our bed in the morning for snuggling or at 4am or..."
Best of luck. I feel for you!