Back to the original question: it depends on what you mean by “defend”. Patent trolls have made millions on just sending out letters asking for money to avoid litigation. If you can find 3-4 knock-offs and get them to give you $50k each with little more than a letter, you’ve already turned a profit.
If your goal is to actually start suing people in the hope that they give you $30 million and cease copying you product, you’ll need deeper pockets.
As for the international aspect, it gets complicated fast. You can get a patent in China, but Chinese law requires you to apply there before any other country. In Canada, you have 5 years after getting a patent in another country to file here (and another 5 years to actually process the patent).
Also, consider shipping. If your knock-off artist ships through your patent country, there are legal process to hold the shipment.