This logic assumes transparent pricing and that bids from international companies not subject to the tax won’t take over Canadian bids forcing prices back up to

This logic assumes transparent pricing and that bids from international companies not subject to the tax won’t take over Canadian bids forcing prices back up to where they were... and I bet multinational organizations would avoid the tax by having US services bid for them. If the tax is on ads shown to Canadians rather than ads paid by Canadian companies, I don’t see how the government can force it short of banning Facebook altogether.