The two substantive provisions are found at proposed sections 349.02 and 349.03.
Proposed section 349.02 prohibits the use of funds
for a partisan activity, for advertising or for an election survey if the source of the funds is a foreign entity.
Then, proposed section 349.03 provides for anti-circumvention provisions and states:
No third party shall
(a) circumvent, or attempt to circumvent, the prohibition under section 349.02; or
(b) act in collusion with another person or entity for that purpose.
Of course, every question is a question of fact, and it's very difficult to assess a specific situation in the void, but the question you've raised about the commingling of money could potentially constitute an “attempt to circumvent” in cases where it is quite obvious that the money was received for this purpose and that it replaced Canadian funds that were diverted to the third party's expenses.