If there were multiple sellers, is each one on the hook for the full indemnity or just their share?

It depends entirely on whether the purchase agreement makes the sellers "joint and several" for indemnity purposes, since there is no automatic default rule under Ontario law making multiple sellers each fully liable, or each liable only for their own share, without the agreement saying so. If the agreement uses joint and several liability language, a buyer can pursue any one of the sellers for the entire indemnity amount, leaving that seller to seek contribution from the others afterward, which gives the buyer significantly stronger practical recourse, especially where one seller has more available assets than the others.

If instead the agreement provides for several, or proportionate, liability, typically tied to each seller's percentage ownership or share of the sale proceeds, each seller's exposure is capped at their own defined share, and the buyer cannot recover a shortfall from one seller by going after another beyond their individual portion. Buyers negotiating a deal with multiple sellers generally prefer joint and several liability for exactly this reason, while sellers, particularly minority sellers, often push for several liability limited to their own proportionate share.