Usually four, if the item was listed on ebay.ca. After that, ebay may send the buyer a Unpaid item Reminder which is code for 'you have four additional days to pay before we put a black mark on your account for not paying your bills'.
If you are the seller, there is an Unpaid Item Assistant feature which automatically allows you to open and close cases at specific intervals. It's in Account Settings.
If you are the buyer, it's best to pay for your item as soon as you are able. By bidding, you have entered into a binding contract. Plus, the seller would genuinely like to send your new purchase to you as soon as is possible. If you have changed your mind about the item, contact the seller as soon as possible. He or she is not obligated to cancel the transaction but if you are very nice and apologetic, they may see fit to do so for you.
Best of luck as you carry forward.