What happens to old liabilities if I buy assets through a brand-new corporation?

Generally, the seller's old liabilities that you didn't expressly assume stay with the seller's corporation, whether your buyer is a brand-new corporation or an existing one — using a new corporation as the buyer doesn't itself change what liabilities transfer. That principle comes from the asset-purchase structure, not from the buyer being newly formed.

The nuance is that a handful of things can still reach even a fresh, newly incorporated buyer. If you hire the seller's employees to keep the business running, Ontario's Employment Standards Act can deem their service continuous, so their accrued entitlements effectively transfer even though your corporation never employed them before. Registered liens against specific equipment or inventory you're buying can also follow the asset itself unless cleared before closing, and if real property is involved, a current owner can face regulatory obligations tied to the land regardless of how new the owning corporation is.

Using a new corporation is a sound way to isolate this acquisition's risk from your other interests, but it isn't a way to avoid the specific liabilities that attach to particular assets or employees you choose to take on. A business lawyer and proper due diligence are what actually manage that.