Q: if i buy a gift card in north america can it be used in south america

No, all iTunes gift cards cards are country-specific, they can only be used in their country of issue and only on accounts with a billing address in that country.

You can use a different countries gift card, if you have an apple id in that country, and it is possible to change it, but billing info has to be changed as well.

To change, go to settings, iTunes & App store, tap apple id....., view apple id, (type password) , country/region, and change it to the country of the gift card, and accept the terms, and change billing info. This is a long process, but it does work. You should then be able to use the gift card.

You need to be in a country to redeem a gift card use its store - the US store's terms of use include (and other countrie will be similar) :

The iTunes Service is available to you only in the United States, its territories, and possessions. You agree not to use or attempt to use the iTunes Service from outside these locations. Apple may use technologies to verify your compliance.

You can't, you can only gift content to people who are in, and whose account is in, the same country as yourself - so you won't be to gift content to people who aren't in Canada nor will they will be able to use Canadian gift cards.

Are they available as printed versions that you could send ?

You can't gift any item from the stores (apps, ibooks etc) to a person in another country. If you buy them on your own account then they will be linked to your account and they would need to be in Canada to redownload them (and they would need your id and password to be able to do so).

Books are only sold where the book publishers have granted Apple to sell them, all content is passed to Apple to sell on a country-by-country basis. You can try requesting that they be added to the Canadian store, but unless the publisher agrees to it then it can't happen : http://www.apple.com/feedback/itunes.html

Also to be able to read most ibooks on a Mac you need OS X Mavericks on it, the majority of ibooks have digital rights management on them which tie them to the iBooks apps i.e. an iPad, iPhone, iPod Touch or a Mac with OS X Mavericks on it (previous OS X versions don't have an iBooks app).

Are they available on other ebook stores e.g. Amazon/Kindle ?