[wildstar]

If you want to go the most absolute fool-proof route, get them Kindle 3s with the 3G access (unless your parents have wi-fi at home and are savvy at connecting to wifi on the road). The 3G service on the Kindle works in Canada and most other countries in the western world.

Yes, if you assign both their kindles to the same account, they can share the books bought on that account. All the books just sit in an "archived" folder on the kindle, synced to the Amazon servers, until your mom or dad decide they want that particular book on their kindle. Amazon is also working on some basic cross-account sharing as well, similar to the Nook.

The Kindle store's prices are in US dollars, so the prevailing exchange rate will affect the price they pay for books, but at the same time you don't pay GST or provincial sales tax.

In terms of selection, the Kindle store has more titles, though if you are into Canadian content, you may have better luck with the Kobo store. You can not for example currently purchase the most recent Giller Prize winner (The Sentimentalists) on Amazon but you can on Kobo.

The keyboard is actually a good thing if they are using the kindle exclusively for browsing the search the bookstore. The onscreen keyboard of the Kobo looks tedious.

The kindles also come with a three-prong plug power cord so you never have to connect it to a computer for charging.

I've got a first generation Kobo and a Kindle 3 and think the Kindle is much better in terms of screen contrast (the text looks pretty close to real print), speed, page turn buttons etc.

I've never used the Nook so can't comment on it.

I would recommend you also get some sort of case as well, regardless of what ereader you end up purchasing.

Hope this helps.