Does it matter for my liability whether I structure the deal as a share deal or an asset deal for a unionized workforce?

It matters, but perhaps not as much as buyers hope. In a share purchase, the same corporate employer continues, so the collective agreement, union recognition, and any grievances or liabilities connected to the unionized workforce simply continue as they already existed, with no separate analysis required.

In an asset purchase, you might expect a cleaner break since you're a new legal entity, but Ontario labour relations law's successor-rights protections exist specifically to prevent an asset structure from being used to avoid an existing union where you're continuing substantially the same operation. So while an asset purchase changes the legal form of the transaction, it doesn't reliably change the labour relations outcome for a unionized workforce the way it can for many other employee-related liabilities, like a specific pre-closing severance debt.

The practical difference between structures narrows considerably once a genuine unionized, going-concern operation is involved. Get a proper assessment of successor-rights exposure specifically, rather than assuming deal structure alone determines your union-related liability the way it might for other employment matters. A Treadstone business lawyer can help you understand where structure actually helps and where it doesn't.