Can I be treated as a successor employer if I only bought some of the business's contracts?

Possibly, yes. Successor employer status under the Employment Standards Act's continuity rule turns on whether you've acquired and are continuing a business, or a distinct part of one, as a going concern — it doesn't require buying literally everything the seller had. Buying a meaningful set of contracts, along with enough of the operational substance to actually carry the business (or a recognizable part of it) forward, can be enough to trigger continuity for employees connected to that part of the business, even if other assets or contracts stayed behind with the seller.

Where this gets genuinely fact-specific is the line between buying "part of a business" in a way that counts, versus simply buying some discrete, non-operating assets or standalone contracts that don't amount to continuing any recognizable part of the seller's operation. The more the deal looks like you're picking up a functioning slice of what the seller was doing, rather than isolated pieces, the more likely continuity applies.

Have your lawyer assess how your specific deal is likely to be characterized before assuming a partial purchase avoids continuity obligations. A Treadstone business lawyer can help evaluate this based on exactly what you're acquiring.