Aside from a brief experiment with Clearview a few years back, Ontario has for ages only used the FHWA type fonts.
That may be true so far as green-background guide signs are concerned, but (per
OTM volume 8) Helvetica is used extensively on certain types of general informatory sign, in cardinal direction tabs (either separate or within combination assemblies), etc. Serifed typefaces are also used on historic landmark signs.
The following sign codes are just a few examples of those that have Helvetica: M112, M114, M115 (combination junction assemblies with provincial crowns, cardinal directions, and arrows), M302, M305, M309, M312 (cardinal direction tabs), M303, M306, M310, M313 (one-piece tabs with both cardinal direction and arrow), M203 ("BUSINESS" tab), M204 ("ENDS") tab, and so on. Oddly enough, there are "JUNCTION," "JCT," and two-headed one-piece tabs with two cardinal directions that do use the FHWA alphabet series.