A Boston is brachycephalic — but less severely than a pug or bulldog
Boston terriers sit at the milder end of the brachycephalic spectrum. Their muzzles are short but not as compressed as a pug's, their tracheas are relatively normal-diameter, and most Bostons cope with moderate heat and exercise better than an English bulldog ever will. That said, they're still short-faced dogs, and the general rules apply: open wire crate rather than solid plastic, room temperature under 75°F for extended crating, and no direct sun on the crate.
The 22" or 24" crate suits most adult Bostons (12–25 lb). Because the breed spans that range widely — some Bostons are truly small at 13 lb, others are stocky at 24 lb — measure your specific dog if you're between sizes.