Concrete Bearing Capacity adjacent Free Edge

Can't help with Canadian codes, but ACI 318-14 Table 22.8.3.2 - Nominal Bearing Strength has entries for "Supporting surface is wider on all sides than the loaded area" and "Other cases." Though it does not state it explicitly, I've always taken this to include concrete with the load on the edge.

If you want to be more thorough, you could look at shear friction along the proposed failure plane. You'll have to assume some perimeter of your failure zone and then see what the plain concrete. Rather than using A[sub]vf[/sub]f[sub]y[/sub] for your normal force, I'd use the load from the door jamb with the appropriate friction coefficient (since you don't have any steel), accounting for the inclined plane.

Baffled Engineer:
Almost zero lateral cap’y. is a pretty good first assumption. I’d weld a couple #3 or 4 rebars to the underside of that jamb base pl. and bend them down at 30 or 45° into the conc. to the right. Then you have some chance of actually calculating some embedment/development length base on real code procedures. Alternatively, embed a .25” or .375” x 3 or 4” by some length bar, with an end hook, bent down into the conc. to the right. Drill this for the jamb A.B., in place, when you know the exact location. This can then be used to drill the hole for the hold down A.B.