I don't have any information about that particular case. I believe C-76 requires third parties to have their own separate bank accounts, so that is one technical way of addressing the transfer of funds.
Constitutionally, you're on very solid ground to restrict spending. The Supreme Court has spoken about that. As for registration and transparency rules, the Supreme Court has spoken about that as well. There is also the question of contribution limits, in terms of donations to political parties and candidates. What's more controversial is whether you could or should have contribution limits for third parties.
Certainly B.C., in its referendum campaign on electoral reform, has limits on how much you can contribute to an advertising sponsor, and I believe this applies to their provincial elections as well. That does have an impact on political expression if you're restricting how much money.... Say a union or a corporation wants to spend its own money as a third party, how do you regulate that as a contribution? There are constitutional questions there but that's one way of addressing the movement of money between different entities, by treating it like a contribution.