Pick the equivalent road ones to your MTB ones, a bit easier with current model lines.
On the Northwave front, I have Shimano XC7 MTB shoes and Northwave Galaxy carbon road shoes the fit is nearly identical. I also use a set of Northwave Hammer SRS for CX as they’ve pretty much got no vents and really grippy soles along with the toe studs.
Giro are ridiculously narrow all round and not very tall in the instep kind of thing.
Personally I would always go for proper road shoes over MTB ones, the pedals clip in far more positively, the platform is nice and you don’t need the massive amount of float you get MTB pedals on the road as (IMHO) you’re not moving around all over the place on the bike.
Best bet is to try them on and get what fits best.