Countries with a strong national identity — linguistic, religious or cultural — are finding it a challenge to effectively integrate people from different backgrounds. In France, there is still a typical citizen and an atypical citizen. Canada doesn’t have that dynamic.
In his mind, having a strong national identity is a kind of hindrance in the modern world of open borders. And I suppose he's right in this assumption. The issue is, do you really want to give up a strong national identity in order to have open borders? Is the loss of identity and connection involved really worth it?
Something that liberals don't seem to get is that having a deep sense of belonging to such communities is part of the framework for developing our personhood (in a more fundamental way than practising tolerance is). We risk losing something significant of ourselves when the opportunity for belonging to such a community is no longer there.