We've done a couple trips with our girls around that age. That time of year is wonderful for taking little ones. My girls did not like characters at that age, DD was 3 before she thought they were okay. It took our 2 year old almost our entire vacation before she would shake Goofy's hand, and she asked to see him every day. She would just freak as we got close. So see how he does, if he loves them then take a ton of pictures. If not, hopefully he'll grow to love them.
If you find he is having a tough time in the stroller then take a break in the Baby Care Centers. They have play rooms, with age appropriate toys where they can have some individual play time. We didn't need to do it but once or twice, but it is really nice.
When the weather was bad my younger DD loved being in a Snugli carrier better than her stroller with a rain cover. I just put on the Snugli, and then carried an umbrella over our heads. She loved the view and was more dry and warm than she would have been in her stroller.
Dress in layers that time of year. It will got from cool in the morning, to warm at lunch, hot in the afternoon to cold at night. We usually put on a onsie with pull on pants and then had a jacket and a blanket and would shed and add back as we needed to.