How would a Canadian government force an American company to be more open?

The same exact way they are doing here - pass a law requiring the company to comply with certain standards if it wants to operate in Canada and lawfully provide services to Canadian customers. Standards that could, for example, include the requirement for all content on the platform to be indexable. Or even to mandate open protocols and federation.

The word used was "open", and you wouldn't be able to force a company to open itself to intellectual theft at the hands of a foreign government. You're reducing a complex legal/rights policy into "wats the problem just do it guys" mentality. You can't even get rights to index something niche, like the Ontario Opera archive catalogue without running into several unions and trade rights representatives. To think that everyone from Google to Netflix could just do this is hilarious.