There are so many good DS-Games that it is difficult to recommend something.
I can't say anything to your first question, because I never played Kirbys Canvas Course, so I can't say if it is any good.
However I played Nintendogs and I liked it. It's really cool, because it uses the Stylus and the Mic of the DS. Sadly I rented my copy to my little niece and haven't seen it since than. (I am pretty sure she hasn't lost it and just don't want to give it back ...). Also you or better your gf must like the style of the game. It's a game which you should play every day for only a few minutes. However if you know that you don't have the time to care for your virtual puppy, because of a vacation for instance, than you can give it into a pension into the game.
Now for some other games I would recommend:
Advance Wars (both parts)
Phoenix Wright (all parts)
Yu-Gi-Oh (the 2008 edition, but only if you like the card game ...)
Zelda
