The provision as drafted says that the act does not apply to an online undertaking, which means none of the provisions of the act would apply if a service fell under that threshold.
The CRTC does have information-gathering powers precisely to be able to assess questions around thresholds. In practice the CRTC should be able to go to a service and ask it to document or show evidence about its revenues in Canada. If that service refused on the basis that by its own assessment it was below this and therefore not subject to the CRTC's information-gathering powers, that would be a question that could potentially be litigated, and I'm not in a position to say how that would necessarily play out in court.