As previously posted, the two big school bus makers are Thomas and Bluebird. Thomas has been owned by Daimler for many years, but Blue Bird remains independent. [See June 2 for more]
Blue Bird will build your bus on any chassis you specify, even the competitor's Freightliner. But just to avoid free advertising, I see they now insert their own badge on the grille - nice moooove!
Photos taken Cap-à-l'Aigle, QC, 2010-08-31.