Not house to house. Some schools take the kids out in groups to go to businesses. Mostly it is a lot of parties. Halloween is not a Belizean holiday per se. San Pedro likes any excuse for a party and has adopted Halloween big-time but you won't find it a notable event elsewhere. The adult costume parties and competitions are over the top. Holiday Hotel has hosted the biggest and baddest for as long as I can remember.
We used to do a door to door trick or treat in the south and would arrange for the neighbors to have treats and be prepared to expect us. But the distances are far between (yes we had fun hanging ghosts and limbs from trees and the like) and the mosquitoes were ferocious. We ended up opting for a centralize Spooky house and a few stops. It was great fun. Wayo's Beach bar hosts a big spooky house halloween party and Saga Humane Society usually holds one for pets. San Pedro does go "all out" for halloween parties.
I found that halloween is an event which regresses in many countries years by years. (Except in USA and some America Latina countries.) I'm French and there are less and less people who celebrate halloween. 10 years ago it was totally different.