Having two boys and potty training them at the same time, I think training boys is the most difficult task. I don't remember your post, but here's how I trained my boys at 3. I put them on a schedule, first every hour they took a potty break until no accidents occur. If they can hold for an hour, I extended potty breaks for 30 minutes until they mastered 1 hr and 30 minutes an so on. During potty break, if your son listens to music that's ok, but I bought a potty book for boys. This is a little cartoon book about a little boy named Henry. Both boys loved it. I would read to them until they went potty or poop. By the time they were potty trained they memorized the book and started to read to me at the end. The trick is consistency, consistency, consistency. I think your son will be trained by the end of July so he might be able to go to preschool. Most boys are potty trained by 3. In the summer, if they are running through the sprinkler I let them go naked and peed outside. I never let them do that inside. Plus, get rid of the huggies underwear, won't let the child know if he had an accident.
Good Luck,
That was the worst having boys was potty training, but eventually, they will get trained.
Oh, he's comfortable standing up..let him. My boys did it too.