Congrats for sticking with it as long as it is intended. The US is the only "westernized" country where breastfeeding is hurried. Most such countries wean at about 3. I personally felt that with my only child close to 3 was cool and I'd not have another chance to breastfeed. We used nursing as close-together-unwinding-time after work and daycare. Forget what other people say about what is age appropriate.
At any rate, one day when my daughter was about 2 1/2, we knew it was not a nourishment thing but a comfort thing so I told her that in a few days she would only drink for a cup and we'd do something else together. That worked.
One day after we came in from a long day at work and daycare as I sat on the sofa, she sat on my lap and raised my shirt. I said, "Remember, we're not nursing anymore. We're using a cup." To which she replied, "I know, I'm just looking at 'em."
Anyway, we didn't have a difficult transition. Perhaps you could cut him down to once a day, as we had at that time. One special time, then exchange the nursing for something else to do to unwind. Talk about how big boys use cups.