Why is the font size of runway numbers in Canada small?
(Click either to view)

Short answer: Canada paints them by the book. They're not small.

Ottawa airport conforms to the standards set by ICAO Annex 14 for airport design. Those standards guarantee the legibility of the numbers.


  5.2.2.6 The numbers and letters shall be in the form and proportion shown in Figure 5-3. The dimensions shall be not less than those shown in Figure 5-3, but where the numbers are incorporated in the threshold marking, larger dimensions shall be used in order to fill adequately the gap between the stripes of the threshold marking.


Member states can deviate and then notify ICAO they have deviated, as long as the height of the characters does not go below 9 meters (30 feet).

There's no answer to why they are smaller than the rest, checking how +250 countries paint the numbers to compare with Canada is unattainable. Canada and many others (Crete, Athens, Cairo, Lisbon, ...) paint them like that, and that's the norm per ICAO.


Measurement from Google Earth for Ottawa.