I guess my answer would be "some, but not too much."
It is very bad if a country gets to be too nationalistic. This can result in really bad thing, up to and beyond wars. Perhaps the clearest example of a war (and worse) that came about because of nationalism was WWII. Both Japan and, especially, Germany were extremely nationalistic. Their attitudes led to terrible atrocities like the Holocaust and the Rape of Nanking.
However, it is fine to have pride in one's country. Having some nationalism helps keep a country together and that is important. This is especially true for multicultural countries like the US and Canada.