Factory speakers are two round ones in the door, one about 5" and one smaller about 2" or 3", so you may not have factory speakers. Best to post a picture. Door speakers don't have much room behind them, so that can be an issue too.
www.crutchfield.com is a good place for checking factory sizes, but first find out what you have now.
Some Japanese cars were imported from the USA, but if its a original Japanese market car (vin has zzz in it) it can cost as much as $10k or more to import to the USA and have it federalized. Canada is much easier, but it would have to go to a citizen for registration.