Temperament for the mounts varies pretty widely, they’re TBs so you have everything from super hot and nutty to quiet enough to do short stirrup in their spare time. Most of the races are either hurdle races (over portable artificial brush fences also called “National” fences or real brush fences) or timber races, over post and rail hunting fences. Hurdle horses sort of jump out of a gallop stride, long and flat, timber horses tend to have a rounder jump more like a show horse.
Race lengths vary but most of the hurdle races are about two miles with the timber races being longer. Jockey weights vary, too, depending on horse age and sex, and the quality of the race (claiming/ allowance/stakes).
AFAIK the furthest north National Steeplechase Association races are in New York-- Genesee Valley is probably closest to Canada along with Saratoga and Belmont. But some hunts have unsanctioned jump races as well.
Around here they are popular with spectators for tailgate parties-- lots of fun extras geared toward kids as well.
www.nationalsteeplechase.com is a good place to start. You can see the conditions (qualifications) for current races here: http://www.nationalsteeplechase.com/wp-content/uploads/pdf/ConditionsBook.pdf