First off, I'd say do it in conversation with a person (not email or voice mail) and face-to-face if possible. That gives you the chance to deliver in full nuance those points you made, that you don't want to look bad through this.
But it depends on many things -- what kind of position (if board approval, I'm thinking it's something fairly high up?) Perhaps you can offer to keep connected a little bit from home, etc. How many are in your group that can provide coverage?
What is the work culture like? In the kinds of jobs I've had (and in Canada in general) there has been a strong sense of work/life balance. Where I've worked, the reaction would be "wow! congratulations! Of course you can get some time off. Family comes first. We'll manage fine without you for a little longer." It wouldn't be paid time off for someone just starting, but arrangements would be made. But I hear many workplaces are all about "productivity", minimal vacation time, and long workdays expected as the default.
I'd see this as a mini-negotiation ... be prepared to be reasonable to meet them partway to keep the employer's most important needs met as much as possible, at the same time being there for your wife and new child in a way you can look back on and be proud of.