I have lived in 4 different places in Belize already, and so far the only two places that take Halloween seriously are San Pedro and Orange Walk.
I can't speak for this year in Orange Walk, but usually the kids go on one massive trick-or-treating. The smaller ones during the day (they contact business establishments and select private homes beforehand) and the bigger kids go out at night. Before the night trick-or-treating, there is a rather large night parade, where everyone (teens and adults) are in costumes and vehicles and floats are decorated with lights and 'scary' decorations. A couple days before Halloween, the local highschools that have their Halloween Fair would parade through the streets of Orange Walk.
In San Pedro, there's no Halloween Parade, but the kids were all over town. I gave bags of assorted candy to over a hundred little kid on behalf of my company (people, possibly local newspapers, were taking pics so no one else wanted to do it lol). It was fun.