Oddly, it is a very small number for transit buses. There's New Flyer and Nova in Canada. Unfortunately, Orion just announced in the last month that they're closing their doors. They were headquartered, by Daimler, in Mississauga, Ontario. So three of the five were located in Canada.
In the United States, you have NABI, in Anniston, Alabama, and GILLIG, in California. So really, there are now, I'd say, four big players in North America.