my son is 31/2...boys are stubborn....he just now is beginning to use the toilet...it is difficult for them to go number 2 on the toilet as i understand..
what worked for us is money....
you could get a post-board and a lot of little stickers...post it near the restroom and eachtime he goes, he gets to put a star on the board....you can work the incentive to your taste...but for each star is a dime, after 10, he gets to trade his dimes for a dollar, then go with the whole family and buys his treat, and even pays himself...
also, letting him be there when mom and dad use the restroom...lots of jumping up and down and clapping is always exciting for these guys...
one more trick of the trade...we bought a brand new pack of pullups and had a new garbage bag in the trash. zacky put one by one in the trash (willingly) and scolded the diapers " bye baby diapers" and " i won't need you anymore" then after he was gone, we took all the items relating to diapers and put them up high...he didn't know there was a stash in the trunk for emergencies, so basically he made a choice...it's all about allowing choices at this age so i learned...at the store he said "mom... i need to go potty!"
now, there has been a few times with grandma and the babysitter that he went number 2 right outside the bathroom...purposly...i don't know if it was because he was upset...i just don't scold for mistakes. ive found that feeding negatve attention seeking brings more rebelous acts than letting them know it's alright..
i hope that this helped somewhat...good luck with all..
p.s.
wait until the day you know that you helped him grow and taught him what unconditional support,love and trust is..it'll be wondorous...
S.