It's likely that the cancelled e-check is the reason for the Unpaid Item Dispute. If you then repaid the same way, the echeck takes upwards of 10 days to clear the Canadian and US banking systems.*
This is one reason why experienced members encourage newbies to back their PP accounts with a credit card instead of a bank account. Faster payments mean happier sellers.
The other reason is that in case of a Item Not Received or Item Not as Described dispute, you have an appeal with the chargeback service of the cc to a PP decision.
*Even if your seller is in Canada, because Paypal's bank is in the USA.